Add Cloudflare Workers deploy config via OpenNext

- Fix build:worker script to use opennextjs-cloudflare build
- Add open-next.config.ts required by OpenNext Cloudflare
- Update wrangler.toml main entry to .open-next/worker.js
- Ignore .open-next/ and .wrangler/ build artifacts

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

open-next.config.ts

@@ -0,0 +1,3 @@
+import { defineCloudflareConfig } from "@opennextjs/cloudflare";
+
+export default defineCloudflareConfig();