fix: dedicate watcher to own worker, fix media auth + memories nav

- Move watch_folders to dedicated 'watcher' queue with its own
  single-concurrency container so it never blocks scan/thumbnail slots
- Add get_current_user_media dependency that accepts ?token= query
  param for <img src> / <video src> media endpoints (thumb, original,
  proxy) — fixes 401 on thumbnails
- Append JWT token to all media URLs in the frontend
- Add missing 'memories' case in sidebar navigation switch

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/LeftSidebar.tsx

@@ -276,6 +276,9 @@ export function LeftSidebar({ onCollapse }: LeftSidebarProps) {
       case 'map':
         navigateToSection('map', {})
         break
+      case 'memories':
+        navigateToSection('memories', {})
+        break
       default:
         if (id.startsWith('folder-')) {
           const folderId = id.slice('folder-'.length)