docs: 複数コードベースのホスト振り分け例を追加 (host routing sample)

[haranishi]

1つのworkerdプロセスで複数のコードベースを動かす実行例を追加します。共通のHTTPソケットから、router Workerがホスト名に応じて2つのアプリへservice bindingでリクエストを転送し、未知のホストには404を返します。

READMEに起動方法、curlでの確認方法、信頼できるコードベース向けの構成であることを記載しました。

Add a runnable example for hosting multiple trusted codebases in one workerd process. A router Worker shares one HTTP socket and forwards requests to two separate application services through service bindings. Unknown hostnames return 404.

The README includes workerd/Bazel startup commands, curl examples, and the trust boundary discussed in #58. Each application has its own modules and compatibility date.

Validation:

• Started the config with the published workerd 2026-04-05 binary.
• Five HTTP checks passed: routing to each application, preserving path/query, unknown-host 404, rejecting a hostname suffix match, and handling an uppercase hostname with a port.
• JavaScript syntax checks and git diff --check passed.
• The native runtime was not rebuilt; this change adds sample files only.

Closes #58.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[haranishi]

recheck