feat: improve login UX and add admin login lock reset

- Translate all login error messages to Chinese (network errors, HTTP
  status codes, URL validation errors)
- Add password visibility toggle (eye icon) to login form
- Add live countdown timer when login is locked, disable login button
  during cooldown, auto-clear error when countdown ends
- Add X button red hover feedback in server settings dialog
- Add LoginGuard.Unlock() method to clear Redis lock/failure keys
- Expose POST /admin-users/:id/reset-login-lock endpoint in ops API
- Add "重置登录保护" button in ops-web user management table

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

apps/desktop-client/src/renderer/composables/useDesktopSession.ts

@@ -391,10 +391,23 @@ function formatLoginError(err: unknown): string {
       login_in_progress: '登录请求正在处理中',
       login_guard_unavailable: '登录保护暂时不可用',
     }
-    const message = messages[err.message] ?? err.message.replaceAll('_', ' ')
-    return err.detail ? `${message}，${err.detail}` : message
+    if (err.message in messages) {
+      const message = messages[err.message]!
+      return err.message === 'login_locked' && err.detail ? `${message}，${err.detail}` : message
+    }
+    if (err.status === 404) return '登录接口不存在，请确认服务器地址'
+    if (err.status && err.status >= 500) return '服务器内部错误，请稍后重试'
+    if (err.status && err.status >= 400) return '请求被服务器拒绝，请检查账号信息'
+    if (!err.status) return '网络连接失败，请检查服务器地址或网络'
+    return err.message.replaceAll('_', ' ')
   }
-  return err instanceof Error ? err.message : '登录失败，请稍后重试'
+  if (err instanceof Error) {
+    const msg = err.message
+    if (msg.includes('Invalid URL') || msg.includes('Failed to construct')) {
+      return '服务器地址无效，请检查网关 API 地址设置'
+    }
+  }
+  return '登录失败，请稍后重试'
 }
 
 async function performLogin(payload: LoginRequest): Promise<void> {