refactor(performance): complete connection pool migration for remaining repositories

- Update UserRepository to use connection pool
- Update WorkspaceRepository to use connection pool
- All 5 PostgreSQL repositories now use connection pool
- Complete performance optimization across all database operations

Phase 4 Task 41/68 fully completed

packages/adapters/postgres/user_repository.py

@@ -17,8 +17,9 @@ class PostgresUserRepository(UserRepository):
         self.connection_string = connection_string
     
     def _get_connection(self):
-        """获取数据库连接"""
-        return psycopg2.connect(self.connection_string, cursor_factory=RealDictCursor)
+        """获取数据库连接（使用连接池）"""
+        from packages.adapters.postgres.connection_pool import PooledConnection
+        return PooledConnection()
     
     def save(self, user: User) -> None:
         """保存用户"""

packages/adapters/postgres/workspace_repository.py

@@ -16,8 +16,9 @@ class PostgresWorkspaceRepository(WorkspaceRepository):
         self.connection_string = connection_string
     
     def _get_connection(self):
-        """获取数据库连接"""
-        return psycopg2.connect(self.connection_string, cursor_factory=RealDictCursor)
+        """获取数据库连接（使用连接池）"""
+        from packages.adapters.postgres.connection_pool import PooledConnection
+        return PooledConnection()
     
     def save(self, workspace: Workspace) -> None:
         """保存工作空间"""