feat: add voice language selection in settings

Add support for users to select voice language preference, which is passed through to ElevenLabs agents via platform settings overrides. Includes new language mapping utilities, UI controls in settings page, and updated voice session initialization.

web/src/lib/locales/zh-CN.ts

@@ -231,6 +231,9 @@ export default {
   'settings.title': '设置',
   'settings.language.title': '语言',
   'settings.language.label': '语言',
+  'settings.voice.title': '语音助手',
+  'settings.voice.language': '语音语言',
+  'settings.voice.autoDetect': '自动检测',
 
   // Misc
   'misc.noMachines': '无可用机器',