fix(ca): translate sql.ErrNoRows to nil,nil for optional lookups

Repository methods that perform single-row queries now return (nil,nil)
instead of leaking sql.ErrNoRows when a row is missing. This aligns with
service-layer expectations (e.g. GetMediaDetail, ValidateSession,
UpdateProgress, AssignTag, access checks) so normal missing data does
not break app flows.

Files changed:
- internal/repository/media.go, user.go, set.go, set_permission.go,
  tag.go, note.go, playback_progress.go, playback_accumulator.go,
  session.go, share.go
- internal/repository/sqlite_test.go (updated assertions)
- internal/repository/sqlite_no_rows_test.go (new focused repository tests)
- internal/service/no_rows_test.go (new focused service tests)

1 files changed, 4 insertions, 1 deletions

diff --git a/internal/repository/playback_progress.go b/internal/repository/playback_progress.go
index 243c8ba..1d05dcd 100644
--- a/internal/repository/playback_progress.go
+++ b/internal/repository/playback_progress.go
@@ -2,6 +2,7 @@ package repository
 
 import (
 	"context"
+	"database/sql"
 	"fmt"
 
 	"github.com/paul/kiss-media-player/internal/model"
@@ -26,7 +27,9 @@ func (s *SQLite) GetProgress(ctx context.Context, userID, mediaID int64) (*model
 		userID, mediaID,
 	)
 	var p model.PlaybackProgress
-	if err := row.Scan(&p.UserID, &p.MediaID, &p.PositionSeconds, &p.UpdatedAt); err != nil {
+	if err := row.Scan(&p.UserID, &p.MediaID, &p.PositionSeconds, &p.UpdatedAt); err == sql.ErrNoRows {
+		return nil, nil
+	} else if err != nil {
 		return nil, err
 	}
 	return &p, nil