chore: 清理 src 下 113 项未使用导入和死代码

删除未使用的文件（BuiltinStatusLine.tsx、4 个重复的 .ts stub）、
移除约 55 个文件中未使用的 React 导入、
清理约 50 处未使用的导入/变量/参数。
净减少 ~296 行代码，precheck 4077 测试全部通过。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/services/mcp/channelNotification.ts

@@ -23,12 +23,10 @@ import { CHANNEL_TAG } from '../../constants/xml.js'
 import { getSubscriptionType } from '../../utils/auth.js'
 import { lazySchema } from '../../utils/lazySchema.js'
 import { parsePluginIdentifier } from '../../utils/plugins/pluginIdentifier.js'
-import { getSettingsForSource } from '../../utils/settings/settings.js'
 import { escapeXmlAttr } from '../../utils/xml.js'
 import {
   type ChannelAllowlistEntry,
   getChannelAllowlist,
-  isChannelsEnabled,
 } from './channelAllowlist.js'
 
 export const ChannelMessageNotificationSchema = lazySchema(() =>

src/services/mcp/client.ts

@@ -117,13 +117,7 @@ import { getLoggingSafeMcpBaseUrl } from './utils.js'
 
 // Package imports — delegate to mcp-client package utilities where applicable
 import {
-  createMcpClient as createMcpClientFromPackage,
-  captureStderr,
   isMcpSessionExpiredError as isMcpSessionExpiredErrorFromPackage,
-  installConnectionMonitor,
-  createCleanup as createCleanupFromPackage,
-  buildConnectedServer,
-  DEFAULT_CONNECTION_TIMEOUT_MS,
   MAX_MCP_DESCRIPTION_LENGTH as PKG_MAX_MCP_DESCRIPTION_LENGTH,
 } from '@claude-code-best/mcp-client'
 import { recursivelySanitizeUnicode } from '@claude-code-best/mcp-client'