feat: unified logging module and remove redundant first_run logic

- Add logger.py with TimedRotatingFileHandler (daily rotation, 30-day retention)
- Replace all print() in migrate.py with logging calls
- Add logging to sync.py for sync status tracking
- Refactor watch.py to use logger.py, remove duplicate first_run branch
- All logs now go to logs/app.log consistently
- Add logging config section to config.yaml, add logs/ to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sync.py

@@ -3,9 +3,12 @@ LAN file sync module.
 Detects file changes, copies from LAN UNC paths to local, and determines which tables need migration.
 """
 
+import logging
 import os
 import shutil
 
+logger = logging.getLogger('app')
+
 
 def sync_file(local_path, lan_path):
     """Sync a single file from LAN to local.
@@ -16,6 +19,7 @@ def sync_file(local_path, lan_path):
     """
     try:
         if not os.path.exists(lan_path):
+            logger.error(f"LAN 路径不可达: {lan_path}")
             return 'error', f'LAN path not accessible: {lan_path}'
 
         lan_mtime = os.path.getmtime(lan_path)
@@ -24,6 +28,7 @@ def sync_file(local_path, lan_path):
         if local_existed:
             local_mtime = os.path.getmtime(local_path)
             if local_mtime == lan_mtime:
+                logger.debug(f"跳过 (mtime一致): {os.path.basename(local_path)}")
                 return 'skipped', None
 
         # Ensure parent directory exists
@@ -41,11 +46,14 @@ def sync_file(local_path, lan_path):
             raise
 
         if not local_existed:
+            logger.info(f"copied: {os.path.basename(local_path)}")
             return 'copied', None
         else:
+            logger.info(f"updated: {os.path.basename(local_path)}")
             return 'updated', None
 
     except Exception as e:
+        logger.error(f"同步失败: {local_path} - {e}")
         return 'error', str(e)