fix: add from __future__ import annotations to workspace_manager.py

Fixes NameError: ToolInstance not defined at runtime because
type annotations are evaluated at class definition time.
Deferring annotation evaluation with __future__ annotations
keeps TYPE_CHECKING imports from causing runtime crashes.

Also includes ruff formatting cleanup on workspace-related files.

apps/api/src/services/workspace_manager.py

@@ -1,5 +1,7 @@
 """Workspace lifecycle management service."""
 
+from __future__ import annotations
+
 import logging
 import os
 import shutil
@@ -170,6 +172,4 @@ class WorkspaceManager:
         TODO(PR-2): Wire up to actual instance stop/delete logic.
         For now, this is a placeholder.
         """
-        logger.warning(
-            "Placeholder: stopping and deleting instance %s", instance.id
-        )
+        logger.warning("Placeholder: stopping and deleting instance %s", instance.id)