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/feishu/feishu-channel.mjs

@@ -2,6 +2,7 @@ import { createHash } from 'node:crypto';
 
 import { trackOutboundArtifactProviderPromise } from '../shared/semantic/artifact.mjs';
 import { createDeliveryReceipt } from '../shared/semantic/delivery.mjs';
+import { t } from '../shared/i18n.mjs';
 
 const STREAM_ELEMENT_ID = 'stream_md';
 const DEFAULT_INITIAL_TEXT = '已连接 DeepSeek Harness，正在思考…';
@@ -133,7 +134,7 @@ function streamingCard(initialText) {
     schema: '2.0',
     config: {
       streaming_mode: true,
-      summary: { content: '正在生成…' },
+      summary: { content: t('正在生成…') },
       streaming_config: {
         print_frequency_ms: { default: 70 },
         print_step: { default: 1 },
@@ -158,12 +159,12 @@ export class VerifiedFeishuChannel {
 
   constructor({
     client,
-    initialText = DEFAULT_INITIAL_TEXT,
+    initialText,
     fileUploadTimeoutMs = MAX_FILE_OPERATION_TIMEOUT_MS,
     fileMessageTimeoutMs = MAX_FILE_OPERATION_TIMEOUT_MS,
   }) {
     this.#client = client;
-    this.#initialText = initialText;
+    this.#initialText = initialText ?? t(DEFAULT_INITIAL_TEXT);
     this.#fileUploadTimeoutMs = boundedFileTimeout(fileUploadTimeoutMs, 'fileUploadTimeoutMs');
     this.#fileMessageTimeoutMs = boundedFileTimeout(fileMessageTimeoutMs, 'fileMessageTimeoutMs');
   }
@@ -215,7 +216,7 @@ export class VerifiedFeishuChannel {
           settings: JSON.stringify({
             config: {
               streaming_mode: false,
-              summary: { content: summaryOf(lastContent) || '回答完成' },
+              summary: { content: summaryOf(lastContent) || t('回答完成') },
             },
           }),
           sequence: ++sequence,