fix: use namespace zod import in house tracker types

`import { z } from 'zod'` is undefined when vitest runs under Bun (as in the
Docker build), matching the earlier fix in eca43c8.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/house-tracker/types.ts

@@ -1,7 +1,7 @@
 // Shared between the home worker (scripts/house-worker.ts), the ingest API and
 // the page. Keep this file free of `#lib` / `$app/env` imports: the worker runs it
 // directly with bun, outside SvelteKit.
-import { z } from 'zod';
+import * as z from 'zod';
 
 export const offers = ['rent', 'buy'] as const;
 export type Offer = (typeof offers)[number];