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/discord/config-store.mjs

@@ -3,6 +3,7 @@ import {
   maskPlatformId,
   TokenBotConfigStore,
 } from '../shared/token-config-store.mjs';
+import { t } from '../shared/i18n.mjs';
 
 const IDENTITY_OPTIONS = Object.freeze({
   botPrefix: 'discord',
@@ -14,7 +15,7 @@ export function deriveDiscordBotIdentity(platformId) {
 }
 
 export function maskDiscordBotId(platformId) {
-  return maskPlatformId(platformId, 'Discord机器人');
+  return maskPlatformId(platformId, t('Discord机器人'));
 }
 
 export class DiscordConfigStore extends TokenBotConfigStore {

src/channels/discord/discord-api.mjs

@@ -1,4 +1,5 @@
 import { createHash } from 'node:crypto';
+import { t } from '../shared/i18n.mjs';
 
 const DEFAULT_BASE_URL = 'https://discord.com/api/v10/';
 const DEFAULT_FILE_UPLOAD_TIMEOUT_MS = 120_000;
@@ -275,7 +276,7 @@ export async function inspectDiscordToken(token, options = {}) {
   if (!bot?.id || bot?.bot !== true) throw new Error('Discord token does not belong to a bot');
   return {
     platformId: String(bot.id),
-    name: cleanString(bot.global_name) ?? cleanString(bot.username) ?? 'Discord机器人',
+    name: cleanString(bot.global_name) ?? cleanString(bot.username) ?? t('Discord机器人'),
     username: cleanString(bot.username),
   };
 }

src/channels/discord/discord-bridge.mjs

@@ -1,9 +1,10 @@
 import { TextHarnessBridge, createTextBridgeStatus } from '../shared/text-harness-bridge.mjs';
+import { t } from '../shared/i18n.mjs';
 
 export const DISCORD_DESCRIPTOR = Object.freeze({
   key: 'discord',
   label: 'Discord',
-  connectionLabel: ' Gateway 长连接',
+  connectionLabel: t(' Gateway 长连接'),
 });
 
 export class DiscordHarnessBridge extends TextHarnessBridge {

src/channels/discord/discord-runtime.mjs

@@ -1,6 +1,7 @@
 import { createEditableMessageStream, splitMessageText } from '../shared/editable-message-stream.mjs';
 import { fetchFileStream } from '../shared/file-download.mjs';
 import { fetchImageBuffer } from '../shared/image-prompt.mjs';
+import { t } from '../shared/i18n.mjs';
 import { DiscordApi } from './discord-api.mjs';
 import { createDiscordBridgeStatus, DiscordHarnessBridge } from './discord-bridge.mjs';
 
@@ -40,12 +41,12 @@ function eventData(event) {
 
 function gatewayCloseError(code) {
   if (code === 4004) {
-    const error = new Error('Discord Bot Token 无效，请重新填写。');
+    const error = new Error(t('Discord Bot Token 无效，请重新填写。'));
     error.code = 'discord-401';
     return error;
   }
   if (code === 4013 || code === 4014) {
-    const error = new Error('Discord Gateway Intents 配置不正确，请检查 Developer Portal 的 Bot 设置。');
+    const error = new Error(t('Discord Gateway Intents 配置不正确，请检查 Developer Portal 的 Bot 设置。'));
     error.code = 'discord-intents';
     return error;
   }