feat: add Cloudflare Workers deployment support

- Create src/worker.ts: Workers-compatible relay handler using env
  bindings instead of process.env, exports { fetch } for Workers runtime
- Update wrangler.toml: point to new src/worker.ts entry point
- Update deploy.yml: add wrangler-action deploy step after tests pass
- The worker reuses the same relay logic from src/lib/ and src/middleware/

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/deploy.yml

@@ -13,3 +13,9 @@ jobs:
       - run: bun install
       - run: bun run build
       - run: bun test
+
+      - name: Deploy to Cloudflare Workers
+        uses: cloudflare/wrangler-action@v3
+        with:
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}