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.

internal/handlers/api/auth_handler.go

@@ -30,9 +30,10 @@ func Login(ctx *gin.Context) {
 	httpx.WriteJSON(ctx, ret)
 }
 
-func AuthOptions(ctx *gin.Context) {
+func PublicConfig(ctx *gin.Context) {
 	cfg := config.Current()
-	httpx.WriteJSON(ctx, &response.AuthOptionsResponse{
+	httpx.WriteJSON(ctx, &response.PublicConfigResponse{
+		Language:      cfg.LanguageOrDefault(),
 		WxWorkEnabled: cfg.WxWork.Enabled,
 		OIDCEnabled:   cfg.OIDC.Enabled,
 	})