refactor: remove LocaleSwitcher component and update locale handling

- Removed LocaleSwitcher from NavUser, SiteHeader, and WorkbenchHeader components.
- Updated tests to reflect the removal of LocaleSwitcher.
- Changed default locale from "en-US" to "zh-CN" in i18n configuration.
- Refactored locale resolution logic to read configured locale without relying on browser language detection.
- Updated AgentDesk SDK to support language configuration from public API.
- Cleaned up unused auth options fetching in the auth API.

web/components/workbench-header.tsx

@@ -5,7 +5,6 @@ import { useRouter } from "next/navigation"
 import { useState } from "react"
 
 import { ChangePasswordDialog } from "@/components/change-password-dialog"
-import { LocaleSwitcher } from "@/components/locale-switcher"
 import { PaletteToggle } from "@/components/palette-toggle"
 import { RealtimeConnectionStatus } from "@/components/realtime-connection-status"
 import { ThemeToggle } from "@/components/theme-toggle"
@@ -36,7 +35,6 @@ export function WorkbenchHeader() {
           <div className="hidden sm:block">
             <RealtimeConnectionStatus status={realtimeStatus} compact />
           </div>
-          <LocaleSwitcher />
           <PaletteToggle />
           <ThemeToggle />
           <WorkbenchUserMenu />