chore(lint): apply ruff --fix (4443 auto-fixes)

Auto-fixed categories:
- F401: unused imports removed
- I001: import blocks sorted
- W293: trailing whitespace stripped
- UP035: deprecated typing imports replaced
- SIM: simplify suggestions applied
- ARG: unused args prefixed with underscore
- T201: print statements removed
- F841: unused variables removed
- RUF059: unpacked variables prefixed

Remaining ~1500 unfixable errors (C901, B904, N806, E402) require manual work.

Backend smoke tests: 13/13 passed.

backend/src/services/git/_sync.py

@@ -5,12 +5,12 @@
 # @RELATION DEPENDS_ON -> [GitServiceUrlMixin]
 
 import os
-from typing import Optional
-from git import Repo
-from git.exc import GitCommandError
+
 from fastapi import HTTPException
+from git.exc import GitCommandError
+
 from src.core.database import SessionLocal
-from src.core.logger import logger, belief_scope
+from src.core.logger import belief_scope, logger
 from src.models.git import GitRepository, GitServerConfig
 
 
@@ -107,7 +107,7 @@ class GitServiceSyncMixin:
                 raise HTTPException(status_code=500, detail=f"Git push failed: {details}")
             except Exception as e:
                 logger.error(f"[push_changes][Coherence:Failed] Failed to push changes: {e}")
-                raise HTTPException(status_code=500, detail=f"Git push failed: {str(e)}")
+                raise HTTPException(status_code=500, detail=f"Git push failed: {e!s}")
     # endregion push_changes
 
     # region pull_changes [TYPE Function]
@@ -167,7 +167,7 @@ class GitServiceSyncMixin:
                 raise
             except Exception as e:
                 logger.error(f"[pull_changes][Coherence:Failed] Failed to pull changes: {e}")
-                raise HTTPException(status_code=500, detail=f"Git pull failed: {str(e)}")
+                raise HTTPException(status_code=500, detail=f"Git pull failed: {e!s}")
     # endregion pull_changes
 # #endregion GitServiceSyncMixin
 # #endregion GitServiceSyncMixin