fix: detect 404 from @kubernetes/client-node v1.x ApiException (FAR-85)

The v1.x ApiException exposes the HTTP status as `code`, not `statusCode`.
Both `isNotFound` (k8s-client) and `isK8s404` (execute) only checked
`statusCode`/`response.statusCode`, so 404s were never recognized:

- `getPvc` re-threw the 404 instead of returning null, which bubbled up
  through `ensureAgentDbPvc` as `k8s_job_create_failed` with the raw
  "persistentvolumeclaims X not found" body — the symptom in FAR-85.
- The PVC was never actually created, because the existence check threw
  before reaching `createPvc`.

Add `code === 404` to both predicates and a regression test for `isK8s404`.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/k8s-client.ts

@@ -178,6 +178,8 @@ export function resetCache(): void {
 function isNotFound(err: unknown): boolean {
   if (!(err instanceof Error)) return false;
   const asAny = err as unknown as Record<string, unknown>;
+  // @kubernetes/client-node v1.x ApiException exposes HTTP status as `code`.
+  if (typeof asAny.code === "number" && asAny.code === 404) return true;
   if (typeof asAny.statusCode === "number" && asAny.statusCode === 404) return true;
   const resp = asAny.response as Record<string, unknown> | undefined;
   return typeof resp?.statusCode === "number" && resp.statusCode === 404;