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>

.gitignore

@@ -35,3 +35,7 @@ report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
 # Added by code-review-graph
 .code-review-graph/
 next-env.d.ts
+
+# OpenNext & Wrangler build output
+.open-next/
+.wrangler/