feat(scanner): add debounced file watching with polling fallback

- Implement event queue with 3-second debouncing for file system events
- Add configurable polling fallback (default 3 min) via SCAN_POLL_INTERVAL_MINUTES
- Add SyncFilesystemWithDatabase to detect orphaned DB entries and new files
- Integrate utils.ResolveMediaURL for consistent media file path resolution
- Add COOKIE_SECURE env var with SameSite=LaxMode for session cookies
- Update media handler to properly decode URL paths for file serving
- Refactor scanner initialization to accept poll interval configuration

internal/handlers/scanner.go

@@ -197,7 +197,7 @@ func (h *Handler) StartWatchModeForLibrary(ctx context.Context, libraryID pgtype
 		folderPaths[i] = folder.FolderPath
 	}
 
-	scanner := services.NewMediaScanner(h.db)
+	scanner := services.NewMediaScanner(h.db, 3)
 	if err := scanner.SetFolders(folderPaths); err != nil {
 		return fmt.Errorf("failed to set scanner folders: %v", err)
 	}