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/qq/qq-runtime.mjs

@@ -4,6 +4,7 @@ import {
   connectionTestTarget,
   connectionTestTargetUnavailable,
 } from '../shared/connection-test.mjs';
+import { t } from '../shared/i18n.mjs';
 import { createQqBridgeStatus, QqHarnessBridge } from './qq-bridge.mjs';
 
 function timeoutError() {
@@ -73,7 +74,7 @@ export class QqRuntime {
 
   async sendConnectionTest(text) {
     if (!this.#status.ready || !this.#bot) {
-      throw connectionTestTargetUnavailable('QQ机器人');
+      throw connectionTestTargetUnavailable(t('QQ机器人'));
     }
     const ownerUserOpenid = typeof this.#config.ownerUserOpenid === 'string'
       ? this.#config.ownerUserOpenid.trim()
@@ -88,7 +89,7 @@ export class QqRuntime {
       : (ownerUserOpenid && ownerUserOpenid !== '*'
         ? { scope: 'c2c', targetId: ownerUserOpenid }
         : null);
-    if (!target) throw connectionTestTargetUnavailable('QQ机器人');
+    if (!target) throw connectionTestTargetUnavailable(t('QQ机器人'));
     await this.#bot.sendText(target, text);
     return { sent: true };
   }