fix(terminal): simplify REST endpoints to use instance_id only

The frontend router navigates to /instances/:instanceId/terminal without
project_id or repo_id. The backend terminal REST endpoints were requiring
these path params, causing 404s.

- Simplify _get_terminal_instance to validate by instance_id only
- Update all REST routes from /projects/{pid}/repositories/{rid}/instances/{iid}/terminal/*
  to /instances/{instance_id}/terminal/*
- Update frontend API client to match new paths
- Update useTerminalSessions hook to take instanceId only
- Update TerminalPage to use simplified hook
- Update tests to match new paths

Fixes: 404 on GET /projects/repositories/instances/{id}/terminal/sessions

apps/web/src/pages/terminal.tsx

@@ -18,9 +18,7 @@ const SESSIONS_TO_INFO = (sessions: TerminalSession[]): TerminalSessionInfo[] =>
 	}));
 
 export const TerminalPage: React.FC = () => {
-	const { projectId, repoId, instanceId } = useParams<{
-		projectId: string;
-		repoId: string;
+	const { instanceId } = useParams<{
 		instanceId: string;
 	}>();
 	const navigate = useNavigate();
@@ -39,7 +37,7 @@ export const TerminalPage: React.FC = () => {
 		resetSession,
 		loading,
 		error,
-	} = useTerminalSessions(projectId ?? "", repoId ?? "", instanceId ?? "");
+	} = useTerminalSessions(instanceId ?? "");
 
 	// Auto-create default session if none exist
 	useEffect(() => {