Add frontend UI for async series loading

- Add SERIES_LOADING_UPDATE WebSocket event
- Update series cards to display loading indicators
- Add real-time status updates via WebSocket
- Include progress tracking (episodes, NFO, logo, images)
- Add CSS styling for loading states
- Implement updateSeriesLoadingStatus function

src/server/web/static/js/shared/constants.js

@@ -26,6 +26,7 @@ AniWorld.Constants = (function() {
         ANIME_RESCAN: '/api/anime/rescan',
         ANIME_STATUS: '/api/anime/status',
         ANIME_SCAN_STATUS: '/api/anime/scan/status',
+        ANIME_LOADING_STATUS: '/api/anime',  // + /{key}/loading-status
 
         // Queue endpoints
         QUEUE_STATUS: '/api/queue/status',
@@ -99,6 +100,9 @@ AniWorld.Constants = (function() {
         SCAN_ERROR: 'scan_error',
         SCAN_FAILED: 'scan_failed',
 
+        // Series loading events
+        SERIES_LOADING_UPDATE: 'series_loading_update',
+
         // Scheduled scan events
         SCHEDULED_RESCAN_STARTED: 'scheduled_rescan_started',
         SCHEDULED_RESCAN_COMPLETED: 'scheduled_rescan_completed',