feat(updater): 定时检查更新与后台自动下载

设置 → 系统新增两个开关：定时检查更新（从不/4/12/24 小时，默认 4）与
自动下载更新（默认关）。安装时机仍交给用户——绝不因下载完成自动退出，
autoInstallOnAppQuit 只覆盖用户自己退出时装上。

- runCheck(source) 统一三条来源（启动/周期/手动），UpdateState.scheduled
  标记来源；已有在途检查返回同一 promise，避免 electron-updater 的去重把
  来源标记记到错的调用方
- 周期调度器经 settingsStore.setUpdateScheduleApplier 注入（updater 已
  import settingsStore，反向 import 成环）；幂等重排，启动检查由
  startupArmed 保证每进程只武装一次；所有 timer 带 unref
- 自动下载由 settings.autoDownloadUpdate 驱动，autoUpdater.autoDownload
  保持 false（单一事实源在 settings）；失败不重试，等下一周期
- 同版本抑制（actedRelease 单槽，actedFor 版本不同即替换）：否则长开机
  的应用每 4 小时重复弹气泡、重复走一遍 downloadUpdate；手动检查无条件
  清空记录
- downloaded 与 fetchHandled 分开：前者仅在 update-downloaded 置位，用于
  阻止后续 update-available 把状态从 downloaded 翻回 available（否则「关于」
  页按钮会从「重启安装」退回「下载」）
- tray.notifyUpdate 弹 Windows 托盘气泡；非 win32 / 无 tray / 有可见窗口
  都不弹

src/main/index.ts

@@ -5,12 +5,12 @@ import { pathToFileURL } from 'url'
 import { devRendererUrl } from './devEnv'
 import { isTrustedRendererUrl, registerIpc } from './ipc'
 import { killAllPtys, killPtysByOwner } from './pty'
-import { applyStartupSystemSettings, loadSettings } from './settingsStore'
+import { applyStartupSystemSettings, loadSettings, setUpdateScheduleApplier } from './settingsStore'
 import { getLockController, initLockController } from './lockController'
 import { applyMenuLockState } from './lockMenu'
 import { isLockBlockedShortcut, isPanicLockChord } from './lockShortcuts'
 import { initTray, markQuitting, onMainWindowClose, refreshTrayMenu } from './tray'
-import { configureAutoUpdater, registerUpdateIpc } from './updater'
+import { applyUpdateSchedule, configureAutoUpdater, registerUpdateIpc } from './updater'
 import { applyWindowChrome } from './windowChrome'
 import { onLanguageChange, t } from '@shared/i18n'
 import { getThemeById } from '@shared/theme'
@@ -90,6 +90,11 @@ if (!gotSingleInstanceLock) {
       // Before the window exists: a renderer-triggered check must not run against
       // the updater's defaults (feed, proxy, autoDownload are set in here).
       configureAutoUpdater()
+      // Arms the startup + periodic update checks and re-arms them on every
+      // settings save. Injected rather than imported by settingsStore because
+      // updater.ts already imports settingsStore: the reverse import would be a
+      // cycle, arming the timer against a half-initialised updater.
+      setUpdateScheduleApplier(applyUpdateSchedule)
       // OS-level effects (login item, sleep blocker) must apply even if the
       // settings dialog is never opened this run.
       applyStartupSystemSettings(loadSettings())