feat: batch favorites endpoint + frontend dedup fixes

Backend:
- Add POST /api/favorites/batch endpoint (single multi-row INSERT)
- Add BatchFavoritesResult/BatchFavoritesStats DTOs
- Add batch methods to ports, service, PG repository
- Transaction-based insert with ON CONFLICT DO NOTHING, chunking at 5000

Frontend:
- Rewrite batchFavorites() to single API call (40 requests → 1)
- Add _replaceCacheFromResponse() to avoid extra GET round-trip
- Centralize formatFileSize, isTextViewable, formatDateTime, formatDateShort
- Remove duplicate icon mapping from app.js
- Fix inconsistent quota defaults (10GB everywhere)

src/interfaces/api/routes.rs

@@ -231,6 +231,7 @@ pub fn create_api_routes(app_state: &AppState) -> Router<AppState> {
 
         Router::new()
             .route("/", get(favorites_handler::get_favorites))
+            .route("/batch", post(favorites_handler::batch_add_favorites))
             .route(
                 "/{item_type}/{item_id}",
                 post(favorites_handler::add_favorite),