fix: resolve macOS build race condition and update download button unresponsive

CI 修复 (electron-builder.yml):
- 移除 mac target 的 arch: [arm64, x64]，改由 CI matrix 的 --arch flag 控制
- 根因：两个 macOS job 各自构建两个架构的 DMG，产生两个 draft release，
  导致 release job 只发布了没有 DMG 的那个，macOS 产物丢失

下载按钮无响应修复:
- electron/updater.ts: downloadUpdate IPC handler 加 try-catch，
  失败时通过 sendStatus 发送 error 事件给前端，避免静默失败
- AppShell.tsx: downloadUpdate 回调点击后立即设置 downloadProgress=0
  提供即时 UI 反馈；加 await + catch 处理下载失败并重置状态
- AppShell.tsx: error 事件处理中重置 downloadProgress 为 null，
  使下载按钮在失败后重新出现
- UpdateDialog.tsx / GeneralSection.tsx: isDownloading 判断移除 > 0 条件，
  downloadProgress === 0 时也显示下载中状态，消除点击后无反馈的间隙

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

electron-builder.yml

@@ -49,7 +49,6 @@ mac:
   artifactName: "${productName}-${version}-${arch}.${ext}"
   target:
     - target: dmg
-      arch: [arm64, x64]
 win:
   icon: build/icon.ico
   target:

electron/updater.ts

@@ -98,7 +98,14 @@ export function initAutoUpdater(win: BrowserWindow) {
   });
 
   ipcMain.handle('updater:download', async () => {
-    return autoUpdater.downloadUpdate();
+    try {
+      return await autoUpdater.downloadUpdate();
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err);
+      console.error('[updater] Download failed:', message);
+      sendStatus({ status: 'error', error: message });
+      throw err;
+    }
   });
 
   ipcMain.handle('updater:quit-and-install', () => {

src/components/layout/AppShell.tsx

@@ -280,6 +280,8 @@ export function AppShell({ children }: { children: React.ReactNode }) {
 
         case 'error':
           setChecking(false);
+          // Reset download progress so the download button re-appears
+          setUpdateInfo((prev) => prev ? { ...prev, downloadProgress: null } : prev);
           console.warn('[updater] Error:', event.error);
           break;
       }
@@ -300,8 +302,16 @@ export function AppShell({ children }: { children: React.ReactNode }) {
     setShowDialog(false);
   }, []);
 
-  const downloadUpdate = useCallback(() => {
-    window.electronAPI?.updater?.downloadUpdate();
+  const downloadUpdate = useCallback(async () => {
+    // Immediately show downloading state so user gets feedback
+    setUpdateInfo((prev) => prev ? { ...prev, downloadProgress: 0 } : prev);
+    try {
+      await window.electronAPI?.updater?.downloadUpdate();
+    } catch (err) {
+      console.warn('[updater] Download failed:', err);
+      // Reset progress so the download button re-appears
+      setUpdateInfo((prev) => prev ? { ...prev, downloadProgress: null } : prev);
+    }
   }, []);
 
   const quitAndInstall = useCallback(() => {

src/components/layout/UpdateDialog.tsx

@@ -20,7 +20,7 @@ export function UpdateDialog() {
   if (!updateInfo?.updateAvailable) return null;
 
   const { isNativeUpdate, readyToInstall, downloadProgress } = updateInfo;
-  const isDownloading = isNativeUpdate && !readyToInstall && downloadProgress != null && downloadProgress > 0;
+  const isDownloading = isNativeUpdate && !readyToInstall && downloadProgress != null;
 
   return (
     <Dialog open={showDialog} onOpenChange={(open) => {

src/components/settings/GeneralSection.tsx

@@ -26,7 +26,7 @@ function UpdateCard() {
   const currentVersion = process.env.NEXT_PUBLIC_APP_VERSION || "0.0.0";
 
   const isDownloading = updateInfo?.isNativeUpdate && !updateInfo.readyToInstall
-    && updateInfo.downloadProgress != null && updateInfo.downloadProgress > 0;
+    && updateInfo.downloadProgress != null;
 
   return (
     <div className="rounded-lg border border-border/50 p-4 transition-shadow hover:shadow-sm">