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/services/cleanup_scheduler.py

@@ -5,7 +5,10 @@ Background scheduler for periodic file cleanup
 
 import asyncio
 import logging
+import os
+import fcntl
 from datetime import datetime
+from pathlib import Path
 from typing import Optional
 
 from sqlalchemy.orm import Session
@@ -16,11 +19,50 @@ from app.services.cleanup_service import cleanup_service
 
 logger = logging.getLogger(__name__)
 
+# Lock file path for multi-worker coordination
+_LOCK_FILE = Path(settings.log_file).parent / ".cleanup_scheduler.lock"
+_lock_fd = None
+
+
+def _try_acquire_lock() -> bool:
+    """
+    Try to acquire exclusive lock for scheduler.
+    Only one worker should run the scheduler.
+    Returns True if lock acquired, False otherwise.
+    """
+    global _lock_fd
+    try:
+        _LOCK_FILE.parent.mkdir(parents=True, exist_ok=True)
+        _lock_fd = open(_LOCK_FILE, 'w')
+        fcntl.flock(_lock_fd.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+        _lock_fd.write(str(os.getpid()))
+        _lock_fd.flush()
+        return True
+    except (IOError, OSError):
+        # Lock is held by another process
+        if _lock_fd:
+            _lock_fd.close()
+            _lock_fd = None
+        return False
+
+
+def _release_lock():
+    """Release the scheduler lock"""
+    global _lock_fd
+    if _lock_fd:
+        try:
+            fcntl.flock(_lock_fd.fileno(), fcntl.LOCK_UN)
+            _lock_fd.close()
+        except Exception:
+            pass
+        _lock_fd = None
+
 
 class CleanupScheduler:
     """
     Background scheduler for periodic file cleanup.
     Uses asyncio for non-blocking background execution.
+    Uses file lock to ensure only one instance runs across multiple workers.
     """
 
     def __init__(self):
@@ -29,6 +71,7 @@ class CleanupScheduler:
         self._last_run: Optional[datetime] = None
         self._next_run: Optional[datetime] = None
         self._last_result: Optional[dict] = None
+        self._has_lock: bool = False
 
     @property
     def is_running(self) -> bool:
@@ -55,9 +98,15 @@ class CleanupScheduler:
             return
 
         if self.is_running:
-            logger.warning("Cleanup scheduler is already running")
+            logger.debug("Cleanup scheduler is already running")
             return
 
+        # Try to acquire lock - only one worker should run the scheduler
+        if not _try_acquire_lock():
+            logger.debug("Another worker is running the cleanup scheduler, skipping")
+            return
+
+        self._has_lock = True
         self._running = True
         self._task = asyncio.create_task(self._run_loop())
         logger.info(
@@ -77,7 +126,11 @@ class CleanupScheduler:
                 pass
             self._task = None
 
-        logger.info("Cleanup scheduler stopped")
+        # Release the lock if we had it
+        if self._has_lock:
+            _release_lock()
+            self._has_lock = False
+            logger.info("Cleanup scheduler stopped")
 
     async def _run_loop(self):
         """Main scheduler loop"""