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/shared/harness-client.mjs

@@ -8,6 +8,7 @@ import {
   InboundFileError,
 } from './inbound-file.mjs';
 import { outboundArtifactRegistry } from './semantic/artifact.mjs';
+import { t } from './i18n.mjs';
 
 // Every channel plugin runs in the same Host process. Sharing ownership by
 // Harness origin prevents two channel-specific clients bound to one Session
@@ -438,7 +439,7 @@ export class HarnessReplyTracker {
       }
 
       if (event.type === 'tool/call') {
-        const name = nonEmptyText(event.data?.name) ?? '工具';
+        const name = nonEmptyText(event.data?.name) ?? t('工具');
         const callId = nonEmptyText(event.data?.callId)
           ?? nonEmptyText(event.data?.subCallId);
         if (callId) this.#toolNames.set(callId, name);
@@ -453,7 +454,7 @@ export class HarnessReplyTracker {
         const error = toolResultErrorText(event.data?.error);
         pushUpdate({
           type: 'status',
-          text: '正在整理结果…',
+          text: t('正在整理结果…'),
           ...(toolName ? { toolName } : {}),
           ...(error ? { error } : {}),
         });