Refactor localization strings to English across various services and UI components

- Updated titles and subtitles in channel_service.go for web channel and WeChat MP channel configurations.
- Changed handoff messages in conversation_human_dispatch_service.go to English.
- Modified notification messages in event handlers for ticket and conversation assignments to English.
- Adjusted ticket creation messages in ticket_service.go to reflect English localization.
- Updated default locale settings in i18n configuration files to English (en-US).
- Changed HTML language attribute in layout.tsx to English.
- Refactored widget locale detection logic in agent-desk-sdk.ts to prioritize English.

web/i18n/config.test.mjs

@@ -25,6 +25,7 @@ async function loadConfig() {
 test("normalizes supported locale aliases", async () => {
   const { DEFAULT_LOCALE, normalizeLocale } = await loadConfig()
 
+  assert.equal(DEFAULT_LOCALE, "en-US")
   assert.equal(normalizeLocale("zh-CN"), "zh-CN")
   assert.equal(normalizeLocale("zh_CN"), "zh-CN")
   assert.equal(normalizeLocale("zh"), "zh-CN")