feat: add loading page with real-time initialization progress

- Create loading.html template with WebSocket-based progress updates
- Update initialization_service to emit progress events via ProgressService
- Modify setup endpoint to run initialization in background and redirect to loading page
- Add /loading route in page_controller
- Show real-time progress for series sync, NFO scan, and media scan steps
- Display completion message with button to continue to app
- Handle errors with visual feedback

src/server/api/auth.py

@@ -30,7 +30,8 @@ async def setup_auth(req: SetupRequest):
     """Initial setup endpoint to configure the master password.
     
     This endpoint also initializes the configuration with all provided values
-    and saves them to config.json.
+    and saves them to config.json. It triggers background initialization
+    and redirects to a loading page that shows real-time progress.
     """
     if auth_service.is_configured():
         raise HTTPException(
@@ -117,17 +118,9 @@ async def setup_auth(req: SetupRequest):
         # Save the config with all updates
         config_service.save_config(config, create_backup=False)
         
-        # Perform initial setup (series sync, NFO scan, media scan)
-        # This ensures everything is initialized immediately after setup
-        # without requiring an application restart
-        from src.config.settings import settings
-        from src.server.services.initialization_service import (
-            perform_initial_setup,
-            perform_nfo_scan_if_needed,
-        )
-        
         # Sync config.json values to settings object
         # (mirroring the logic in fastapi_app.py lifespan)
+        from src.config.settings import settings
         other_settings = dict(config.other) if config.other else {}
         if other_settings.get("anime_directory"):
             settings.anime_directory = str(other_settings["anime_directory"])
@@ -142,12 +135,53 @@ async def setup_auth(req: SetupRequest):
             settings.nfo_download_fanart = config.nfo.download_fanart
             settings.nfo_image_size = config.nfo.image_size
         
-        # Perform the initial series sync and mark as completed
-        await perform_initial_setup()
+        # Trigger initialization in background task
+        import asyncio
+
+        from src.server.services.initialization_service import (
+            perform_initial_setup,
+            perform_nfo_scan_if_needed,
+        )
+        from src.server.utils.dependencies import get_progress_service
         
-        # Perform NFO scan if configured
-        await perform_nfo_scan_if_needed()
+        progress_service = get_progress_service()
         
+        async def run_initialization():
+            """Run initialization steps with progress updates."""
+            try:
+                # Perform the initial series sync and mark as completed
+                await perform_initial_setup(progress_service)
+                
+                # Perform NFO scan if configured
+                await perform_nfo_scan_if_needed(progress_service)
+                
+                # Send completion event
+                progress_service.emit_progress(
+                    progress_id="initialization_complete",
+                    progress_type="system",
+                    status="completed",
+                    title="Initialization Complete",
+                    message="All initialization tasks completed successfully",
+                    percent=100,
+                    metadata={"initialization_complete": True}
+                )
+            except Exception as e:
+                # Send error event
+                progress_service.emit_progress(
+                    progress_id="initialization_error",
+                    progress_type="error",
+                    status="failed",
+                    title="Initialization Failed",
+                    message=str(e),
+                    percent=0,
+                    metadata={"initialization_complete": True, "error": str(e)}
+                )
+        
+        # Start initialization in background
+        asyncio.create_task(run_initialization())
+        
+        # Return redirect to loading page
+        return {"status": "ok", "redirect": "/loading"}
         # Note: Media scan is skipped during setup as it requires
         # background_loader service which is only available during
         # application lifespan. It will run on first application startup.