fix: workspace delete MissingGreenlet + nginx cache-busting

- Convert WorkspaceHasInstancesError to store plain dicts instead of
  SQLAlchemy ORM objects, preventing lazy-load failures outside async
  session context (MissingGreenlet)
- Update both delete endpoints (top-level and nested) to use exc.instances
  directly since they're already plain dicts
- Add no-cache headers for index.html in nginx.conf so browsers always
  fetch new hashed JS/CSS bundles on deploy

apps/api/src/services/workspace_manager.py

@@ -37,7 +37,7 @@ class SyncResult:
 class WorkspaceHasInstancesError(Exception):
     """Raised when attempting to delete a workspace with running instances."""
 
-    def __init__(self, instances: list[ToolInstance]) -> None:
+    def __init__(self, instances: list[dict]) -> None:
         self.instances = instances
         super().__init__(f"Workspace has {len(instances)} running tool instance(s)")
 
@@ -139,7 +139,9 @@ class WorkspaceManager:
 
         instances = await self._get_instances(workspace, session)
         if instances and not force:
-            raise WorkspaceHasInstancesError(instances)
+            raise WorkspaceHasInstancesError(
+                [{"id": str(i.id), "name": i.name} for i in instances]
+            )
 
         # Stop and delete all instances
         for instance in instances: