fix: workspace delete mixed-content error via top-level endpoint

- Add top-level DELETE /workspaces/{workspace_id} endpoint (avoids nested path)
- Frontend deleteWorkspace now uses /workspaces/{id}/?force=... (no project/repo needed)
- Update useWorkspaceActions, ProjectsPage, WorkspacesPage to match new signature

Quality gates: ruff clean, tsc --noEmit clean, pytest workspaces API (9 passed, 1 skipped)

apps/api/src/services/git_service.py

@@ -147,7 +147,9 @@ class GitService:
                 os.unlink(key_path)
 
     @staticmethod
-    def branch_exists_remotely(path: str, branch: str, ssh_key: str | None = None) -> bool:
+    def branch_exists_remotely(
+        path: str, branch: str, ssh_key: str | None = None
+    ) -> bool:
         """Check if a branch exists on the remote.
 
         Args: