feat: 新增第 8 个内置 tab「文件追踪」——移植 dsh-file-trace 插件

- 数据层：直接折叠会话事件日志(tool/call + tool/result 对)提取文件操作，
  与仓库「读事件日志而非动注册表」的取向一致；含错误文本捕获与
  running 态实时更新(ctx.on('session/event')，不可见时暂停、恢复时追平)
- 视图：操作列表 + 底部可拖拽 diff 面板；行级 diff(删红/增绿/改蓝)+
  行内字符级高亮；读取视图带真实行号；失败操作统一展示真实错误文本
- 语法着色：轻量分词器(关键字/字符串/数字/类型/函数/注释/预处理)，
  色相经 color-mix 落在 diff 三色之间的空档；跨行块注释状态按行序推导
- 单实例 tab，+ 菜单 order 55，角标显示操作数；设置页可整体关闭
  (与独立维护的 dsh-file-trace 插件共存)
- i18n：10 个新 key 同步全部 21 个词典；builtins 测试 7→8；
  README/指南内置清单同步

tests/builtins.spec.ts

@@ -1,5 +1,5 @@
 /**
- * Built-in registration tests: the plugin registers 7 tabs and 6 file
+ * Built-in registration tests: the plugin registers 8 tabs and 6 file
  * viewers through the same service external plugins use (dogfooding);
  * the catch-all `code` viewer, the NUL-sniffing `binary-download` viewer,
  * and the html sandbox settings pin the registry's behavior. (Office
@@ -27,13 +27,22 @@ function setup(options: BuiltinTabOptions = {}): { service: ReturnType<typeof cr
 }
 
 describe('built-in tab registrations', () => {
-  it('registers the 7 built-in tabs', () => {
+  it('registers the 8 built-in tabs', () => {
     const { service } = setup()
     expect(service.getTabs().map(t => t.id).sort()).toEqual(
-      ['browser', 'diff', 'editor', 'git', 'sidechat', 'subagent', 'terminal'],
+      ['browser', 'diff', 'editor', 'file-trace', 'git', 'sidechat', 'subagent', 'terminal'],
     )
   })
 
+  it('the file-trace tab is a single-instance badge-carrying visible tab', () => {
+    const { service } = setup()
+    const trace = service.getTab('file-trace')
+    expect(trace?.single).toBe(true)
+    expect(trace?.hidden).not.toBe(true)
+    expect(trace?.badge).toBeDefined()
+    expect(trace?.component).toBeDefined()
+  })
+
   it('only diff is hidden from the + menu; editor is the visible files window (order 10)', () => {
     const { service } = setup()
     expect(service.getTabs().filter(t => t.hidden).map(t => t.id)).toEqual(['diff'])