feat: add storage cleanup mechanism with soft delete and auto scheduler

- Add soft delete (deleted_at column) to preserve task records for statistics
- Implement cleanup service to delete old files while keeping DB records
- Add automatic cleanup scheduler (configurable interval, default 24h)
- Add admin endpoints: storage stats, cleanup trigger, scheduler status
- Update task service with admin views (include deleted/files_deleted)
- Add frontend storage management UI in admin dashboard
- Add i18n translations for storage management

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/main.py

@@ -216,6 +216,15 @@ async def lifespan(app: FastAPI):
     except Exception as e:
         logger.warning(f"Failed to initialize prediction semaphore: {e}")
 
+    # Initialize cleanup scheduler if enabled
+    if settings.cleanup_enabled:
+        try:
+            from app.services.cleanup_scheduler import start_cleanup_scheduler
+            await start_cleanup_scheduler()
+            logger.info("Cleanup scheduler initialized")
+        except Exception as e:
+            logger.warning(f"Failed to initialize cleanup scheduler: {e}")
+
     logger.info("Application startup complete")
 
     yield
@@ -223,6 +232,15 @@ async def lifespan(app: FastAPI):
     # Shutdown
     logger.info("Shutting down Tool_OCR application...")
 
+    # Stop cleanup scheduler
+    if settings.cleanup_enabled:
+        try:
+            from app.services.cleanup_scheduler import stop_cleanup_scheduler
+            await stop_cleanup_scheduler()
+            logger.info("Cleanup scheduler stopped")
+        except Exception as e:
+            logger.warning(f"Error stopping cleanup scheduler: {e}")
+
     # Connection draining - wait for active requests to complete
     await drain_connections(timeout=30.0)