feat: video support + Memories music choices

Videos:
- Worker ingests .mp4 .mov .m4v .avi .mkv .webm .3gp via ffmpeg/ffprobe
  (frame extract → sharp resize, same thumbnail pipeline as photos)
- DB: media_type + duration columns with migration
- GET /api/videos returns all indexed videos
- GET /api/photos/:id/video streams original file with Range support
  for browser seek/scrub
- VideosView: 16:9 thumbnail grid, play-button overlay, duration badge
- Full-screen player: native <video controls>, ESC to close
- Library tab now excludes videos (dedicated Videos tab)
- Dockerfile: adds ffmpeg to runtime stage

Memories music choices:
- Three styles: ⚡ Upbeat (G-major, default), 🌙 Dreamy (A-minor),
  🎬 Cinematic (D-minor, dual-oscillator richness)
- Shared Web Audio engine (reverb, LPF, pad + melody)
- Style picker in header; active style icon shown in slideshow bar

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

client/src/api/photos.js

@@ -109,6 +109,11 @@ export function triggerSync(source) {
   return api(`/api/sync/${source}`, { method: 'POST' });
 }
 
+// Videos
+export function fetchVideos() {
+  return api('/api/videos');
+}
+
 // Memories
 export function fetchMemories() {
   const d = new Date();