feat: Phase 9 — Dashboard web embarqué

- Frontend vanilla JS (18.9KB) : dark theme, gallery grid, search, stats, WebSocket
- rust-embed : frontend servi depuis le binaire (zéro dépendance externe)
- API REST fonctionnelle : /api/health, /api/images, /api/search, /api/images/:id, /api/stats
- WebSocket hub (dashmap + broadcast) : notifications temps réel
- ImagoClient: méthode get_raw() pour proxy thumbnails, Serialize sur ImageInfo
- MIME guess pour servir CSS/JS/images avec bons headers
- Fallback SPA : routes inconnues → index.html
- Dépendances : tokio-stream, futures-util, dashmap, chrono
- Testé : health OK, stats JSON, dashboard 18.9KB HTML, WS upgrade 400 (HTTP)

0 errors, 0 warnings (cargo check + build --release)

Cargo.toml

@@ -40,6 +40,12 @@ tower = "0.5"
 tower-http = { version = "0.6", features = ["cors", "fs", "trace"] }
 # Frontend embedding
 rust-embed = "8"
+# WebSocket broadcast
+tokio-stream = "0.1"
+futures-util = "0.3"
+dashmap = "6"
+# Time formatting
+chrono = { version = "0.4", features = ["serde"] }
 
 # Platform-specific — Windows
 [target.'cfg(windows)'.dependencies]