feat!: 合并 Git 面板与文件追踪为统一「文件变动」tab（双视角 + 统一 diff 栈）

在 PR #471（file-trace）基础上的演进：

- 合并 tab：git tab（id 保留，兼容持久化布局）升级为「文件变动」双视角
  tab——Git 视角（原 GitView 全部能力：staged/unstaged/提交/历史/worktree·
  子仓库选择/右键菜单/确认弹窗）+ 本轮文件视角（原 file-trace：会话事件
  日志实时折叠的模型读写编辑记录，按文件分组、新增类型筛选 chips、相对
  时间）；file-trace tab 移除（未随任何版本发布）。
- 统一 diff 组件：新 src/client/diff/ 模块（rows.ts 引擎 + DiffRows/
  DiffFiles 渲染器 + highlight.ts 语法着色）——git diff 与会话操作 diff
  共用一套渲染：mod 改写配对（del-run/add-run 对半标蓝）、行内字符级
  高亮（修复了旧实现旧侧失配不高亮的问题，改为行对象身份键）、上下文
  hunk 折叠、git hunk 间未输出区间按行号范围生成不可展开折叠、语法着色
  色相落位 diff 三色空档、+n −m 统计 chips、行底色 tint；DiffTab 改用
  该栈（git diff tab 从此也有高亮）。
- 交互：两视角共用底部可拖拽预览面板（点击文件/提交/操作即预览，不再
  直接开 diff tab；面板可刷新、可键盘/拖拽调高、git 目标可一键展开为
  独立 diff tab）；视角选择与面板高度持久化在 tab.meta；git 行 XY 徽章
  按状态字母着色；选中行高亮。
- i18n：fileTrace* 十键重命名为 changes* 前缀，git 键值更新为「文件
  变动」，新增 7 键（视角/筛选/面板操作），全部 21 个词典同步。
- 结构：src/client/changes/（ChangesTab/GitLens/SessionLens/DiffPane/
  ops）+ src/client/diff/；GitView/DiffView/filetrace/ 删除；git 样式
  从 sidebar.module.css 迁至 changes.module.css。
- 测试：builtins 8→7（git tab 承接 badge pin）、diff-rows（unified
  转换/mod 配对/间隙折叠/统计）、changes-tab（壳交互 jsdom）、
  diff-files-collapse（原 DiffView 折叠行为钉住）、changes-ops（原
  filetrace 数据层）、git-view-worktree 迁移至 GitLens；全量 1122 通过。
- 文档：README ×2 功能矩阵合并、external-plugin-guide §4.4 与内置清单
  7 tab、mount e2e 菜单标题同步。

tests/diff-rows.spec.ts

@@ -0,0 +1,123 @@
+/**
+ * The unified-diff adapter: git's own hunks (from parseUnifiedDiff) convert
+ * into the shared DiffRow segments — rewrite pairing applies inside git
+ * hunks exactly like session-op diffs, the unemitted context gaps between
+ * hunks become non-expandable folds carrying their line ranges, and the
+ * header stats (+n −m) count mods on both sides.
+ */
+import { describe, expect, it } from 'vitest'
+import { parseUnifiedDiff, unifiedSegments, diffLines, pairMods, diffStats, untrackedFile } from '../src/client/diff/rows.ts'
+
+const twoHunks = [
+  'diff --git a/a.ts b/a.ts',
+  '--- a/a.ts',
+  '+++ b/a.ts',
+  '@@ -1,4 +1,4 @@',
+  ' context',
+  '-old line',
+  '+new line',
+  ' tail',
+  '@@ -20,3 +20,4 @@',
+  ' far below',
+  '-gone',
+  '+kept',
+  '+added',
+  ' tail2',
+].join('\n')
+
+describe('unifiedSegments', () => {
+  it('converts hunk lines to rows and pairs the rewrite as mod', () => {
+    const file = parseUnifiedDiff(twoHunks).files[0]!
+    const segments = unifiedSegments(file)
+    // hunk, gap fold (lines 4..19 hidden), hunk
+    expect(segments.map(s => s.kind)).toEqual(['hunk', 'fold', 'hunk'])
+    const first = segments[0]!
+    expect(first.kind === 'hunk' && first.rows.map(r => r.kind)).toEqual(['context', 'mod', 'mod', 'context'])
+    // The paired rows keep their own side's line number.
+    const modOld = first.kind === 'hunk' ? first.rows[1]! : undefined
+    const modNew = first.kind === 'hunk' ? first.rows[2]! : undefined
+    expect(modOld?.oldLine).toBe(2)
+    expect(modOld?.newLine).toBeUndefined()
+    expect(modNew?.oldLine).toBeUndefined()
+    expect(modNew?.newLine).toBe(2)
+  })
+
+  it('emits a non-expandable fold for the unemitted gap between hunks', () => {
+    const file = parseUnifiedDiff(twoHunks).files[0]!
+    const gap = unifiedSegments(file)[1]!
+    expect(gap.kind).toBe('fold')
+    if (gap.kind === 'fold') {
+      expect(gap.rows).toBeUndefined()
+      // First hunk ends at line 3 on both sides, second starts at 20 → gap 16.
+      expect(gap.count).toBe(16)
+      expect(gap.oldStart).toBe(4)
+      expect(gap.oldEnd).toBe(19)
+      expect(gap.newStart).toBe(4)
+      expect(gap.newEnd).toBe(19)
+    }
+  })
+
+  it('emits a leading fold when the first hunk starts below line 1', () => {
+    const diff = [
+      'diff --git a/a.ts b/a.ts',
+      '--- a/a.ts',
+      '+++ b/a.ts',
+      '@@ -10 +10 @@',
+      '-old',
+      '+new',
+    ].join('\n')
+    const file = parseUnifiedDiff(diff).files[0]!
+    const segments = unifiedSegments(file)
+    expect(segments.map(s => s.kind)).toEqual(['fold', 'hunk'])
+    const lead = segments[0]!
+    if (lead.kind === 'fold') {
+      expect(lead.count).toBe(9)
+      expect(lead.rows).toBeUndefined()
+    }
+  })
+
+  it('carries the no-newline marker as a meta row', () => {
+    const diff = [
+      'diff --git a/a.ts b/a.ts',
+      '--- a/a.ts',
+      '+++ b/a.ts',
+      '@@ -1 +1 @@',
+      '-old',
+      '\\ No newline at end of file',
+      '+new',
+    ].join('\n')
+    const file = parseUnifiedDiff(diff).files[0]!
+    const rows = unifiedSegments(file).flatMap(s => (s.kind === 'hunk' ? s.rows : []))
+    expect(rows.map(r => r.kind)).toEqual(['del', 'meta', 'add'])
+    expect(rows[1]).toMatchObject({ kind: 'meta', text: ' No newline at end of file' })
+  })
+
+  it('counts header stats with mods on both sides', () => {
+    const file = parseUnifiedDiff(twoHunks).files[0]!
+    // Hunk 1 pairs 1 del + 1 add (2 mod rows); hunk 2 pairs 1 of its 1 del
+    // with 1 of its 2 adds (2 mod rows) leaving 1 pure add: 5 added, 4 deleted.
+    expect(diffStats(unifiedSegments(file))).toEqual({ added: 5, deleted: 4 })
+    // A full-file addition (untracked fallback) counts every row once.
+    const untracked = untrackedFile('new.ts', 'a\nb\n')
+    expect(diffStats(unifiedSegments(untracked))).toEqual({ added: 2, deleted: 0 })
+  })
+})
+
+describe('pairMods', () => {
+  it('pairs only the overlapping del/add rows within one run', () => {
+    const rows = pairMods([
+      { kind: 'context' as const, oldLine: 1, newLine: 1, text: 'x' },
+      { kind: 'del' as const, oldLine: 2, text: 'a' },
+      { kind: 'del' as const, oldLine: 3, text: 'b' },
+      { kind: 'add' as const, newLine: 2, text: 'B' },
+      { kind: 'add' as const, newLine: 3, text: 'c' },
+      { kind: 'add' as const, newLine: 4, text: 'd' },
+    ])
+    expect(rows.map(r => r.kind)).toEqual(['context', 'mod', 'mod', 'mod', 'mod', 'add'])
+  })
+
+  it('matches diffLines output (the LCS walk pairs rewrites the same way)', () => {
+    const rows = diffLines('hello world', 'hello dsh')
+    expect(rows.map(r => r.kind)).toEqual(['mod', 'mod'])
+  })
+})