build: configure Cloudflare Pages deployment

- Add wrangler CLI and workerd runtime as dev dependencies
- Configure nitro prerender with autoSubfolderIndex disabled for Pages
- Add Turnstile validation endpoint for server-side CAPTCHA verification
- Add baseline-browser-mapping for browser compatibility

pnpm-workspace.yaml

@@ -5,3 +5,4 @@ onlyBuiltDependencies:
   - sharp
   - unrs-resolver
   - vue-demi
+  - workerd