add WebGL scenes to all themes, sounds, image sizing, new themes

- All 11 themes now have unique Three.js WebGL backgrounds:
  aurora: flowing sine-wave ribbon meshes with additive blending
  brutalist: harsh rotating white/red wireframe boxes
  glass: drifting crystal icosahedron shards, semi-transparent
  matrix: digital rain particle columns with per-vertex colour fade
  ocean: animated vertex-displaced wave surface with orbiting light
  retro: amber demo-scene cube with orbiting octahedrons
  synthwave: sunset sphere with scan-line rings and perspective grid
  terminal: green icosahedron wireframe with orbiting torus particles
  neon: existing Three.js orb and rings (unchanged)
  plasma (replaces minimal): drifting additive-blend colour blobs
  volcano (replaces paper): rising ember particles with lifecycle

- shared.go: distinct sounds for j/k nav (220Hz beep), Enter (ascending
  triangle chime), and Esc (descending sine sweep)
- shared.go: images are now thumbnails (max-height:220px) in list view
  and expand to full width inside the modal (CSS override in navmodal)
- main.go: --list-themes flag prints all theme names and exits;
  --theme random picks a random theme at all generation time
- themes.go: updated registry with plasma/volcano replacing minimal/paper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/cmd/snonux/main.go b/cmd/snonux/main.go
index 5a9c9d3..58d6cb5 100644
--- a/cmd/snonux/main.go
+++ b/cmd/snonux/main.go
@@ -11,8 +11,10 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"math/rand"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"codeberg.org/snonux/snonux/internal/config"
 	"codeberg.org/snonux/snonux/internal/generator"
@@ -31,15 +33,29 @@ func main() {
 }
 
 // parseFlags reads CLI flags and returns a validated Config.
+// Special theme value "random" picks a theme at random from the registry.
 func parseFlags() (*config.Config, error) {
 	cfg := &config.Config{}
+	listThemes := flag.Bool("list-themes", false, "print all available theme names and exit")
 
 	flag.StringVar(&cfg.InputDir, "input", "./inbox", "directory containing new source files to process")
 	flag.StringVar(&cfg.OutputDir, "output", "~/git/snonux.foo/dist", "root directory for generated static site output")
 	flag.StringVar(&cfg.BaseURL, "base-url", "https://snonux.foo", "canonical base URL used in Atom feed links")
-	flag.StringVar(&cfg.Theme, "theme", "neon", "visual theme: aurora, brutalist, glass, matrix, minimal, neon, ocean, paper, retro, synthwave, terminal")
+	flag.StringVar(&cfg.Theme, "theme", "neon", "visual theme name, or \"random\" to pick one at random")
 	flag.Parse()
 
+	if *listThemes {
+		fmt.Println(strings.Join(generator.ListThemes(), "\n"))
+		os.Exit(0)
+	}
+
+	// Resolve the special "random" value before any further validation.
+	if cfg.Theme == "random" {
+		themes := generator.ListThemes()
+		cfg.Theme = themes[rand.Intn(len(themes))]
+		log.Printf("random theme selected: %s", cfg.Theme)
+	}
+
 	var err error
 
 	cfg.InputDir, err = expandHome(cfg.InputDir)