feat: 重构 WebSearch/WebFetch，新增 Tavily 适配器及 /web-tools 面板

- WebSearch: 默认 Tavily，适配器优先级 WEB_SEARCH_ADAPTER > settings.webSearchAdapter > tavily
- WebFetch: 支持 Tavily /extract 返回 Markdown，移除 domain blacklist 远程检查
- 新增 /web-tools 命令面板（Search/Fetch 双 Tab + 二级配置菜单）
- 新增 settings 字段: webSearchAdapter, webFetchAdapter, tavilyEndpointUrl, braveApiKey, exaApiKey, exaEndpointUrl, webFetchHttpTimeoutMs
- 适配器联动: Tavily/Exa 从 settings 读取 endpoint 和 API key

Co-Authored-By: deepseek-v4-pro <deepseek-ai@claude-code-best.win>

src/commands.ts

@@ -60,6 +60,7 @@ import terminalSetup from './commands/terminalSetup/index.js'
 import usage from './commands/usage/index.js'
 import theme from './commands/theme/index.js'
 import vim from './commands/vim/index.js'
+import webTools from './commands/web-tools/index.js'
 import { feature } from 'bun:bundle'
 // Dead code elimination: conditional imports
 /* eslint-disable @typescript-eslint/no-require-imports */
@@ -363,6 +364,7 @@ const COMMANDS = memoize((): Command[] => [
   usage,
   usageReport,
   vim,
+  webTools,
   ...(webCmd ? [webCmd] : []),
   ...(forkCmd ? [forkCmd] : []),
   ...(buddy ? [buddy] : []),