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/api/openai/client.ts

@@ -2,7 +2,6 @@ import OpenAI from 'openai'
 import { openaiAdapter } from 'src/services/providerUsage/adapters/openai.js'
 import { updateProviderBuckets } from 'src/services/providerUsage/store.js'
 import { getProxyFetchOptions } from 'src/utils/proxy.js'
-import { isEnvTruthy } from 'src/utils/envUtils.js'
 
 /**
  * Environment variables:

src/services/api/openai/index.ts

@@ -9,8 +9,6 @@ import type {
 } from '../../../types/message.js'
 import type { AgentId } from '../../../types/ids.js'
 import type { Tools } from '../../../Tool.js'
-import type { Stream } from 'openai/streaming.mjs'
-import type { ChatCompletionCreateParamsStreaming } from 'openai/resources/chat/completions/completions.mjs'
 import { getOpenAIClient } from './client.js'
 import {
   anthropicMessagesToOpenAI,