fix: logging, warnings, and soft-delete consistency

- Fix duplicate logging in multi-worker mode with file lock for cleanup scheduler
- Add Pydantic V2 model_config to suppress protected_namespaces warning
- Suppress PaddlePaddle ccache warnings
- Fix admin.py using non-existent User.username (now uses email)
- Fix get_user_stats to exclude soft-deleted tasks from statistics
- Fix create_task to exclude soft-deleted tasks from user limit check
- Change LOG_LEVEL default to INFO

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

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

backend/app/routers/admin.py

@@ -401,7 +401,7 @@ async def trigger_cleanup(
         result = cleanup_service.cleanup_all_users(db, max_files_per_user=files_to_keep)
 
         logger.info(
-            f"Manual cleanup triggered by admin {admin_user.username}: "
+            f"Manual cleanup triggered by admin {admin_user.email}: "
             f"{result['total_files_deleted']} files, {result['total_bytes_freed']} bytes"
         )