fix(middleware): prevent premature redirect to /login during loading

Users were incorrectly redirected to /login during the initial loading phase
before the loading was actually complete. Added loading_started and
loading_complete flags to properly track the initialization state so
the setup redirect middleware knows when it's safe to redirect.

src/server/services/initialization_service.py

@@ -383,6 +383,16 @@ async def perform_initial_setup(progress_service=None):
         # Mark the initial scan as completed
         await _mark_initial_scan_completed()
 
+        # Mark loading as complete in config (used by middleware to allow redirect to /login)
+        try:
+            from src.server.services.config_service import get_config_service
+            config_svc = get_config_service()
+            init_config = config_svc.load_config()
+            init_config.other['loading_complete'] = True
+            config_svc.save_config(init_config, create_backup=False)
+        except Exception as e:
+            logger.warning("Failed to save loading_complete flag: %s", e)
+
         # Load series into memory from database
         await _load_series_into_memory(progress_service)