refactor: optimize database session lifecycle and middleware architecture

- Improve database pool capacity logging with detailed configuration parameters
- Optimize database session dependency injection with middleware-managed lifecycle
- Simplify plugin middleware by delegating session creation to FastAPI dependencies
- Fix import path in auth routes (relative to absolute)
- Add safety checks for database session management across middleware exception handlers
- Ensure session cleanup only when not managed by middleware (avoid premature cleanup)

src/core/batch_committer.py

@@ -46,6 +46,11 @@ class BatchCommitter:
 
     def mark_dirty(self, session: Session):
         """标记 Session 有待提交的更改"""
+        # 请求级事务由中间件统一 commit/rollback；避免后台任务在请求中途误提交。
+        if session is None:
+            return
+        if session.info.get("managed_by_middleware"):
+            return
         self._pending_sessions.add(session)
 
     async def _batch_commit_loop(self):