fix(cleanup-release): 正式版與預發行版分組各自保留 KEEP_COUNT，避免 beta 擠掉正式版

- release 依 prerelease 欄位拆成正式版與預發行版兩組，各自保留最新 KEEP_COUNT 筆
- tag 保護名單改由兩組保留者聯集產生，被保留版本的 tag 一律不清除
- log 新增 STABLE_COUNT／PRERELEASE_COUNT 方便追蹤兩組數量
- action.yml 更新 KEEP_COUNT 參數說明為兩組各自保留

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

src/index.js

@@ -395,7 +395,7 @@ function hasBatchFailure(results) {
 }
 
 /**
- * 執行 release 與 tag 清理流程。
+ * 執行 release 與 tag 清理流程；正式版與預發行版（prerelease）分組計算，各自保留最新 `KEEP_COUNT` 筆。
  */
 async function main() {
   const GITEA_SERVER_URL = normalizeEnvValue(process.env.GITEA_SERVER_URL);
@@ -454,16 +454,21 @@ async function main() {
     return 0;
   });
 
-  const releaseCount = releaseJson.length;
-  info(`RELEASE_COUNT=${releaseCount}`);
+  const stableReleases = releaseJson.filter((item) => !item?.prerelease);
+  const preReleases = releaseJson.filter((item) => item?.prerelease);
+
+  info(`RELEASE_COUNT=${releaseJson.length}`);
+  info(`STABLE_COUNT=${stableReleases.length}`);
+  info(`PRERELEASE_COUNT=${preReleases.length}`);
   info(`KEEP_COUNT=${KEEP_COUNT}`);
 
-  if (releaseCount <= keepCount) {
+  const releaseToKeep = [...stableReleases.slice(0, keepCount), ...preReleases.slice(0, keepCount)];
+  const releaseToDelete = [...stableReleases.slice(keepCount), ...preReleases.slice(keepCount)];
+
+  if (releaseToDelete.length === 0) {
     info('沒有需要清理的舊版本成品');
   } else {
     section('刪除舊版本成品');
-
-    const releaseToDelete = releaseJson.slice(keepCount);
     const releaseResults = await processInBatches(releaseToDelete, DELETE_CONCURRENCY, async (releaseItem) => {
       const releaseId = releaseItem?.id;
       if (!Number.isSafeInteger(releaseId) || releaseId <= 0) {
@@ -496,8 +501,7 @@ async function main() {
   section('刪除未指定 release 的 tag');
 
   const releaseTags = new Set(
-    releaseJson
-      .slice(0, keepCount)
+    releaseToKeep
       .map((item) => item?.tag_name)
       .filter((tag) => !isEmptyOrNull(tag)),
   );