refactor(release-cleanup): 將清理邏輯由 bash 改寫為 Node.js 模組

依功能分組為 logger/validate/config/gitea-client/releases/tags 模組,
entrypoint.sh 改為呼叫 node /app/index.js,Dockerfile 改用 node:20-alpine 基底。
對外行為(清理舊 release 與未指定 release 的 tag)維持不變。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/index.js

@@ -0,0 +1,22 @@
+// 進入點:載入設定、建立 Gitea 客戶端,依序清理舊成品與孤立 tag。
+
+import { loadConfig } from './config.js'
+import { GiteaClient } from './gitea-client.js'
+import { cleanupReleases } from './releases.js'
+import { cleanupOrphanTags } from './tags.js'
+import { separator, fail } from './logger.js'
+
+async function main() {
+  const config = loadConfig()
+  const client = new GiteaClient({ token: config.token })
+
+  await cleanupReleases(client, config)
+  await cleanupOrphanTags(client, config)
+
+  separator()
+}
+
+main().catch((error) => {
+  fail(error.message)
+  process.exit(1)
+})