docs: create AGENTS.md documentation

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+# KISS Media Player — Agent Documentation
+
+This file is written for coding agents working on the `kiss-media-player` project.
+
+---
+
+## Architecture Overview
+
+The project is a **self-hosted media player** designed for simplicity (KISS): minimal dependencies, no frontend frameworks, interface-driven Go code for easy testing.
+
+### Backend
+
+- **Language / Runtime:** Go 1.23
+- **HTTP Server:** `net/http` stdlib only; `http.ServeMux` with pattern matching
+- **Database:** SQLite via `modernc.org/sqlite`
+- **Media Processing:** `ffmpeg` / `ffprobe` installed in runtime container
+- **Password Hashing:** `golang.org/x/crypto/bcrypt`
+
+**Layered architecture:**
+
+| Layer | Package | Role |
+|-------|---------|------|
+| Entrypoint | `cmd/mediaplayer` | Flags, config, dependency wiring, server start |
+| API / Transport | `internal/api` | `Server` struct holds `http.ServeMux`, route table, middleware, handlers |
+| Service | `internal/service` | Business logic: `MediaService`, `AdminService`, `ProgressService`, `GCWorker` |
+| Repository | `internal/repository` | `Store` interface (composite of per-entity repos); concrete SQLite in `sqlite.go` |
+| Domain | `internal/model` | Pure structs (`Media`, `User`, `Set`, `Session`, etc.) — zero external deps |
+| Utilities | `internal/auth`, `internal/scanner`, `internal/probe`, `internal/thumb`, `internal/clock`, `internal/setassign` | Hasher, session manager, filesystem scanner, ffprobe wrapper, thumbnail generator, clock abstraction, permission helper |
+
+All external dependencies are injected via constructors (e.g., `NewServer`, `NewMediaService`, `NewFSScanner`). Hand-written mocks live in `internal/repository/mock.go` and `internal/service/mock.go`.
+
+### Frontend
+
+- **Stack:** Vanilla ES modules, no bundler or build step
+- **Pages:** `index.html` (SPA), `login.html`, `bootstrap.html`
+- **Styling:** CSS Custom Properties (`var(--*)`) defined in `web/css/theme.css`; utility/component/layout styles in separate files
+- **PWA:** `manifest.json` + `web/sw.js` caches static assets for offline usage
+- **Media Player:** HTML5 `<video>` / `<audio>` with a custom overlay control bar
+- **Routing:** Simple page-type switch in `app.js` based on `location.pathname`
+
+### Build & Deploy
+
+- **Build Tool:** Mage (`Magefile.go`)
+- **Container:** Multi-stage `Dockerfile` (Go builder → Alpine runtime with `ffmpeg`)
+- **Kubernetes:** `Deployment` + `Service` + two PVCs (`/data` for DB, `/media` for library)
+
+---
+
+## Running Tests
+
+```bash
+# Run all tests with race detector and coverage
+go test ./... -race -cover
+
+# Generate coverage profile and view it
+go test ./... -race -coverprofile=coverage.out && go tool cover -func=coverage.out
+```
+
+Tests use:
+- `:memory:` SQLite instances for repository-layer tests
+- Hand-written mocks (fakes) for service-layer tests
+- `httptest` + mocked services for handler tests
+- Golden JSON fixtures for `probe` tests
+
+---
+
+## Mage Targets
+
+Install `mage` if you don't have it already:
+
+```bash
+go install github.com/magefile/mage@latest
+```
+
+Available targets (from `Magefile.go`):
+
+| Target | Description |
+|--------|-------------|
+| `mage` (default) | Same as `mage build` |
+| `mage build` | Compile the binary (`go build -o play ./cmd/mediaplayer`) |
+| `mage test` | Run `go test ./...` |
+| `mage install` | Build and copy `play` to `$GOPATH/bin` (or `~/go/bin`) |
+| `mage clean` | Remove the `play` binary |
+| `mage docker-build` | Build container image as `kiss-media-player:latest` |
+| `mage docker-push` | Push `kiss-media-player:latest` to registry |
+
+---
+
+## Kubernetes Deployment
+
+The `k8s/` directory contains:
+
+| File | Resource |
+|------|----------|
+| `k8s/deployment.yaml` | `Deployment` (1 replica, non-root `65534:65534`, probes) |
+| `k8s/service.yaml` | `ClusterIP` Service on port 8080 |
+| `k8s/pvc-db.yaml` | `PersistentVolumeClaim` (`ReadWriteOnce`, 1Gi) for `/data` |
+| `k8s/pvc-media.yaml` | `PersistentVolumeClaim` (`ReadWriteMany`, 10Gi) for `/media` |
+| `k8s/secret.yaml` | `Secret` (optional) for environment overrides (e.g., `ADMIN_PASSWORD`) |
+
+Deploy everything:
+
+```bash
+kubectl apply -f k8s/
+```
+
+The `Deployment` overrides two critical settings for K8s:
+- `DB_PATH=/data/media.db`
+- `MEDIA_ROOT=/media`
+
+Probes:
+- **Liveness:** `GET /healthz` (no DB dependency)
+- **Readiness:** `GET /readyz` (DB ping)
+
+Security:
+- `runAsNonRoot: true`
+- `runAsUser: 65534` / `runAsGroup: 65534`
+- `allowPrivilegeEscalation: false`
+- `readOnlyRootFilesystem: true`
+
+---
+
+## Theming Guide
+
+All colors live in `web/css/theme.css` as CSS Custom Properties on `:root`.
+
+### Current Implementation
+
+`themes.js` swaps the active theme by setting `document.documentElement.setAttribute('data-theme', ...)` and saves the preference to `localStorage`. Override blocks in `theme.css` handle the light variant:
+
+```css
+/* Default (dark) — defined on :root */
+:root {
+  --bg-body: #0f1117;
+  --text-primary: #e6e8ef;
+  --accent: #5e9eff;
+  ...
+}
+
+/* Light theme overrides */
+[data-theme="light"] {
+  --bg-body: #f4f5f8;
+  --text-primary: #12131a;
+  --accent: #2b6cb0;
+  ...
+}
+```
+
+### Adding a New Theme
+
+Option A — inline override (recommended for small additions):
+
+1. Open `web/css/theme.css`.
+2. Append a new attribute selector after the light block, e.g.:
+
+```css
+[data-theme="solarized"] {
+  --bg-body: #002b36;
+  --text-primary: #839496;
+  --accent: #268bd2;
+  ...
+}
+```
+
+3. Wire the toggle in `web/js/themes.js` (or expose a selector UI in `index.html`) to call `apply('solarized')`.
+
+Option B — separate file (if you prefer a stylesheet swap):
+
+1. Create `web/css/themes/<name>.css` containing `:root { ... }` overrides.
+2. Dynamically create or swap a `<link rel="stylesheet">` in `themes.js` instead of using `data-theme`.
+
+**Rules:**
+- No color literals in component styles — everything must go through `var(--*)`.
+- Do not add inline styles in HTML or JS.
+
+---
+
+## Keyboard Shortcuts
+
+Global shortcuts are registered in `web/js/keyboard.js`. They are **disabled** while the user is focused on an `INPUT`, `TEXTAREA`, or `contentEditable` element (except `Escape` to blur).
+
+| Key | Action |
+|-----|--------|
+| `↑` / `↓` | Navigate media list (up / down) |
+| `k` / `j` | Navigate media list (up / down) |
+| `←` / `→` | Switch sets / pages |
+| `h` / `l` | Switch sets / pages |
+| `Enter` | Open selected media (navigate to detail) |
+| `Space` / `p` | Play / pause / switch to selected item |
+| `f` | Toggle fullscreen on the player wrapper |
+| `Esc` | Exit fullscreen, or deselect current item |
+| `r` | Toggle shuffle on the current filtered result set |
+| `s` | Generate a share link for the selected media |
+| `/` | Focus the quick search bar (debounced) |
+| `n` | Open notes modal for the selected media |
+
+---
+
+## Admin Tasks
+
+Admin endpoints are gated by `RequireAdmin` middleware (checks `users.is_admin`). The admin panel is opened via the hidden "Admin" button in the SPA header (shown only when the current user is an admin).
+
+### Creating Users
+
+1. Open the admin panel.
+2. Enter username, password, and check "Is admin" if desired.
+3. Submit — the frontend calls `POST /api/admin/users`.
+4. Admins cannot delete themselves via `DELETE /api/admin/users/:id`.
+
+### Managing Set Permissions
+
+- `GET /api/admin/permissions` — list permissions matrix
+- `POST /api/admin/permissions` — grant access to a set (`body: { set_id, user_id, role: "owner" | "viewer" }`)
+- `DELETE /api/admin/permissions` — revoke access (`body: { set_id, user_id }`)
+
+Roles:
+- `owner` — can upload to the set, soft-delete / restore media, regenerate thumbnails
+- `viewer` — can browse and play media in the set
+
+Admins implicitly see all sets without explicit permission rows.
+
+### Rescanning the Library
+
+Click **Rescan** in the admin panel, or call:
+
+```bash
+curl -X POST -b session=<cookie> http://<host>/api/admin/rescan
+```
+
+This triggers `FSScanner.Scan()`, which:
+1. Scans immediate subdirectories of `MEDIA_ROOT` as **sets**
+2. Recursively walks each set for supported media files
+3. Probes new files with `ffprobe`
+4. Generates thumbnails for video files
+5. Inserts new records into the `media` table
+
+---
+
+## Configuration via Environment Variables
+
+`internal/config.go` loads all settings from the environment.
+
+| Variable | Default | Validation | Description |
+|----------|---------|------------|-------------|
+| `PORT` | `8080` | 1–65535 | HTTP listen port |
+| `MEDIA_ROOT` | `./media` | — | Root path for media set directories |
+| `DB_PATH` | `data.db` | — | SQLite database file path |
+| `MAX_UPLOAD_SIZE_MB` | `100` | ≥ 1 | Max upload size per file (MB) |
+| `SESSION_TIMEOUT_HOURS` | `24` | ≥ 1 | Cookie / session expiry |
+| `GC_INTERVAL_MINUTES` | `30` | ≥ 1 | Garbage collector tick interval |
+| `SHARE_DEFAULT_EXPIRY_DAYS` | `7` | ≥ 1 | Default share link lifetime |
+| `LOG_LEVEL` | `info` | `debug` / `info` / `warn` / `error` | Log verbosity |
+
+**Important:** The K8s `Deployment` overrides `DB_PATH` to `/data/media.db` and `MEDIA_ROOT` to `/media` so the PVC mounts are used. Do not rely on the local defaults in a container.
+
+---
+
+## Notes for Agents
+
+- When modifying tests, always run `go test ./... -race -cover` before committing.
+- Do not introduce package-level mutable state; inject via constructors.
+- All repository access goes through the `repository.Store` interface.
+- Frontend modules are plain ES modules — no transpilation step. Keep JS vanilla.
+- CSS changes must use `var(--*)` tokens from `theme.css`.
+- If you add new env vars, update both `internal/config.go` and this document.
diff --git a/PLAN.md b/PLAN.md
index b405015..a51fa79 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -76,8 +76,8 @@ A self-hosted, Kubernetes-deployable web media player written in Go (stdlib `net
 │   │   ├── player.css       # Custom overlay, fullscreen progress-bar-visible
 │   │   ├── layout.css       # Responsive grid/flex
 │   │   ├── login.css        # Login page layout
-│   │   └── themes/
-│   │       └── light.css    # Future swap
+  │   │   └── themes/        # (empty; themes toggled via data-theme in theme.css)
+
 │   └── js/
 │       ├── app.js           # Router, auth bootstrap, orchestration
 │       ├── api.js           # Fetch wrapper (credentials: include)
@@ -330,13 +330,13 @@ CREATE INDEX idx_shares_expires ON shares(expires_at);
 
 ### 9. Upload
 - `POST /api/sets/:id/upload` with `multipart/form-data`.
-- Max file size: **500MB** (`MAX_UPLOAD_SIZE_MB=500`).
+- Max file size: **100MB** (`MAX_UPLOAD_SIZE_MB=100`).
 - If filename exists, append `(1)`, `(2)`, etc.
 - After save, immediate `ffprobe` + `ffmpeg` thumbnail + insert into `media`.
 
 ### 10. Share Links
 - `POST /api/media/:id/shares` generates a new random token.
-- Default expiration: **14 days** from now.
+- Default expiration: **7 days** from now.
 - Public routes `/s/:token` and `/s/:token/stream` bypass auth.
 - Each time `s` is pressed, a **new share** is created (old ones remain valid until expiry).
 
@@ -344,7 +344,7 @@ CREATE INDEX idx_shares_expires ON shares(expires_at);
 - `DELETE /api/media/:id` sets `deleted_at = NOW()`.
 - Media hidden from normal views; shown in admin trash view.
 - Admin/owner can restore before 7 days.
-- Background goroutine (`time.Ticker` hourly) selects items where `deleted_at < NOW() - 7 days`.
+- Background goroutine (`time.Ticker`, default every 30 minutes) selects items where `deleted_at < NOW() - 7 days`.
 - Physical file deleted via `os.Remove()`, then **hard DELETE** from DB row.
 
 ### 12. Thumbnail Regeneration
@@ -396,12 +396,12 @@ CREATE INDEX idx_shares_expires ON shares(expires_at);
 | Variable | Default | Description |
 |----------|---------|-------------|
 | `PORT` | `8080` | HTTP listen port |
-| `MEDIA_ROOT` | `/media` | Root path for set directories |
-| `DB_PATH` | `/data/media.db` | SQLite database file |
-| `MAX_UPLOAD_SIZE_MB` | `500` | Max upload size per file |
+| `MEDIA_ROOT` | `./media` | Root path for set directories |
+| `DB_PATH` | `data.db` | SQLite database file |
+| `MAX_UPLOAD_SIZE_MB` | `100` | Max upload size per file |
 | `SESSION_TIMEOUT_HOURS` | `24` | Cookie expiry |
-| `GC_INTERVAL_MINUTES` | `60` | Garbage collector tick |
-| `SHARE_DEFAULT_EXPIRY_DAYS` | `14` | Default share link lifetime |
+| `GC_INTERVAL_MINUTES` | `30` | Garbage collector tick |
+| `SHARE_DEFAULT_EXPIRY_DAYS` | `7` | Default share link lifetime |
 | `LOG_LEVEL` | `info` | Log verbosity |
 
 ---
@@ -440,7 +440,7 @@ All 31 features implemented, tested, and deployable:
 17. Theming (CSS variables)
 18. Dark Mode Toggle
 19. Upload (500MB, owner/admin)
-20. Share Links (s key, 14 days)
+20. Share Links (s key, 7 days)
 21. Shuffle (r key, filtered scope)
 22. Keyboard Navigation
 23. Selection Highlight