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/renderer/views/LoginView.vue

@@ -105,7 +105,7 @@ onBeforeUnmount(() => {
         <div class="brand-logo">
           <span class="brand-core"></span>
         </div>
-        <h1 class="brand-name">GEO Rankly</h1>
+        <h1 class="brand-name">省心推</h1>
       </header>
 
       <form class="login-form" @submit.prevent="submitLogin">