fix(updater,i18n): 对抗性审查修复（1中 + 3低）

- [中] 手动检查不再丢弃「已下载」事实：runCheck('manual') 原来无条件清
  抑制记录，导致下载完成后点「检查更新」会把关于页从「重启安装」退回
  「下载」（包已在磁盘）。改为保留 downloaded 记录，只清 announcement
  记账；测试 §19 补 manual-check 保持 downloaded 的口径（153 断言）
- website 首帧脚本：?lang= 的 decodeURIComponent 包 try/catch（畸形转义
  会在 IIFE 内抛 URIError，跳过 html[lang] 与防闪标记，指定语言被静默
  忽略）；zh-Hant-TW/zh-Hant-HK/zh-Hant 按 BCP-47 语义判为繁体
  （normalize 与 i18n-apply.js 双处同步）
- ZmodemOffers 是 App 兄弟节点，语言切换时父级 children bailout 不重渲染：
  订阅 language 并以 tFor 显式翻译（事件回调内的 t() 保留）
- ROADMAP 补录对抗性审查推迟项（周期检查可被设置写入推迟、启动开关
  即时生效语义、下载无整体超时、--channel-only/--skip-gitea 矛盾）

src/main/updater.ts

@@ -323,11 +323,17 @@ async function performCheck(source: CheckSource): Promise<UpdateState> {
  */
 export function runCheck(source: CheckSource = 'manual'): Promise<UpdateState> {
   // A manual check is an explicit act, so whatever it finds counts as news even
-  // if this run has already dealt with that version: the suppression record is
-  // dropped here — before the in-flight guard, so a click that joins a check
-  // already running gets the same treatment. (A manual DOWNLOAD needs no
-  // equivalent: its entry point never consults the record.)
-  if (source === 'manual') actedRelease = undefined
+  // if this run has already announced that version: the announcement half of the
+  // record is dropped here — before the in-flight guard, so a click that joins a
+  // check already running gets the same treatment. The DOWNLOADED half is kept:
+  // for a release whose package sits on disk, "downloaded" *is* the truthful
+  // answer, and dropping it made update-available report `available` again —
+  // folding the About tab's install button back into "download" for a manual
+  // check on an already-fetched release. (A manual DOWNLOAD needs no equivalent:
+  // its entry point never consults the record.)
+  if (source === 'manual') {
+    actedRelease = actedRelease?.downloaded ? actedRelease : undefined
+  }
   if (checkInFlight) return checkInFlight
   const task = performCheck(source)
   checkInFlight = task