feat(i18n): add English support for host-side chat messages

Wrap all user-facing chat text in src/channels with a host-side t()
translator (Chinese is the identity default, so untranslated text is
always sent verbatim in Chinese). English is selected via the host
plugin config `language: en` or the DSH_IM_LANGUAGE environment
variable, and the settings UI keeps following the DSH web locale.

- add src/channels/shared/i18n.mjs with setImHostLanguage/t() and a
  Chinese-key -> English dictionary split by area (shared + channels)
- complete the English dictionary for every t() key in src/channels,
  including the feishu channel (welcome/help, repair flow, interactive
  cards, watch flow) and the shared command/approval/stream text
- wrap previously untranslated chat-facing strings in feishu bridge,
  feishu runtime, editable-message-stream, harness-client,
  connection-test and image-prompt
- dedupe dictionary entries that existed in multiple channel files and
  canonicalize conflicting translations into the shared dictionaries
- extend the i18n unit test to decode string-literal escapes so keys
  containing \n are checked correctly
- document the language switch in README.md, README.en.md and
  CHANGELOG.md, and rebuild lib/index.js

Added English support for bot chat messages across all nine IM
channels and AI Office without changing any Chinese output.

src/channels/dingtalk/dingtalk-api.mjs

@@ -2,6 +2,7 @@ import { randomUUID } from 'node:crypto';
 import { extname } from 'node:path';
 
 import { fetchImageBuffer, ImagePromptError } from '../shared/image-prompt.mjs';
+import { t } from '../shared/i18n.mjs';
 
 export const DINGTALK_REGISTRATION_BASE_URL = 'https://oapi.dingtalk.com/';
 export const DINGTALK_API_BASE_URL = 'https://api.dingtalk.com/';
@@ -829,7 +830,7 @@ export function createDingtalkApi({
             clientId: appKey,
             clientSecret: appSecret,
             cardInstanceId,
-            text: '消息处理失败，请稍后重试。',
+            text: t('消息处理失败，请稍后重试。'),
             signal: cleanupSignal,
           }).catch(() => undefined);
         }