fix: workspace creation with stale directories and missing bind mount

- workspace_manager.py: remove stale workspace directories before cloning
  to prevent 'already exists' errors from previous failed attempts
- workspaces.py: add ValueError -> 400 handling, keep 409 for duplicates
- test_tool_instances_legacy.py: fix broken patches for new helpers
  (get_container_name removed, _ensure_backend_network_in_compose added,
  workspace_id/ssh_key_ids mock attributes added)
- docker-compose.traefik.yml: add /data/working-copies bind mount

Quality gates: pytest (19 passed, 1 skipped)

apps/api/src/api/workspaces.py

@@ -232,6 +232,12 @@ async def create_workspace(
         workspace = await manager.create(repo, user_id, name, branch, session=session)
         session.add(workspace)
         await session.commit()
+    except HTTPException:
+        raise
+    except ValueError as exc:
+        await session.rollback()
+        logger.error("Failed to create workspace: %s", exc)
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
     except Exception as exc:
         await session.rollback()
         logger.error("Failed to create workspace: %s", exc)