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/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),
   };
 }