chore: rebrand product as 省心推 and lock UI to zh-CN

Update server titles, web/desktop window/tray/document titles, login
copy, and electron build metadata to use the Chinese product name 省心推.
Drop the runtime locale switcher and en-US import — the app now ships
zh-CN only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/main/tray.ts

@@ -57,7 +57,7 @@ export function updateTrayIssueIndicator(issueCount: number): void {
 
   tray.setImage(createTrayIcon(hasIssues ? "danger" : "normal"));
   tray.setTitle(hasIssues ? formatIssueCount(safeCount) : "", { fontType: "monospacedDigit" });
-  tray.setToolTip(hasIssues ? `GEO Rankly Desktop · ${safeCount} 个账号健康问题` : "GEO Rankly Desktop");
+  tray.setToolTip(hasIssues ? `省心推 · ${safeCount} 个账号健康问题` : "省心推");
 }
 
 export function initTray(onOpen: () => void): ElectronTray {