feat: Git 面板真正的 diff 显示 + VSCode 式历史与右键高级操作，v0.3.0

- 真正的统一 diff 显示：hunk 头 + 双行号 + 红绿着色，长行换行无横向滚动，untracked 全新增视图
- 点击变更/历史自动打开独立 diff tab（首次在下半栏新增分栏，同变更去重聚焦，临时页签刷新不恢复）
- 历史行：分支徽章 + 作者/相对时间，懒加载分页（20 条/页 + 加载更多）
- 右键菜单：文件行（打开/暂存/放弃更改/复制路径）、历史行（复制哈希/信息/还原/捡取），破坏性操作确认弹窗
- 修复暂存/未暂存分类错误（' M' 被误标为已暂存导致 diff 恒空）
- 修复 git 相对路径解析（会话在仓库子目录时 diff/discard/show/read 可用）
- host 新增 git.commit-diff / git.discard / git.revert / git.cherry-pick 路由与 log 分页

src/client/DiffTab.tsx

@@ -0,0 +1,110 @@
+/**
+ * The diff tab: one change opened from the git panel, like VSCode's diff
+ * editor. A worktree ref loads the file's unified diff (`git diff`, staged or
+ * not; untracked files — which git diff never covers — render as a full-file
+ * addition from their content), a commit ref loads the commit's full patch
+ * (`git.show`-style). The header carries a refresh button because the tab
+ * stays mounted while the git panel's staging/discard operations change the
+ * very content it shows.
+ */
+import { useCallback, useEffect, useState } from 'react'
+import { IconRefreshOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
+import type { SessionScope } from './api.ts'
+import { api } from './api.ts'
+import type { SidebarDiffRef } from './state.ts'
+import { DiffView } from './DiffView.tsx'
+import { t } from './locales.ts'
+import css from './sidebar.module.css'
+
+/** The loaded diff surface (untracked content rendered as a full addition). */
+interface DiffData {
+  diff: string
+  untracked?: string
+}
+
+export function DiffTab(props: { sessionId: string; cwd: string | undefined; diff: SidebarDiffRef }) {
+  const { sessionId, cwd, diff } = props
+  const [loading, setLoading] = useState(true)
+  const [error, setError] = useState<string | null>(null)
+  const [data, setData] = useState<DiffData | null>(null)
+  const [tick, setTick] = useState(0)
+
+  const refresh = useCallback((): void => { setTick(value => value + 1) }, [])
+
+  useEffect(() => {
+    let cancelled = false
+    const scope: SessionScope = { sessionId, cwd }
+    setLoading(true)
+    setError(null)
+    setData(null)
+    const load = async (): Promise<void> => {
+      try {
+        if (diff.kind === 'commit') {
+          const result = await api.gitCommitDiff(scope, diff.hashFull)
+          if (!cancelled) setData({ diff: result.diff })
+          return
+        }
+        let result = await api.gitDiff(scope, diff.path, diff.staged)
+        if (result.diff === '') {
+          // The requested side is empty — try the OTHER side once: the ref
+          // may predate the staged-flag fix, or the change moved sides (a
+          // file staged after its tab opened). Both sides empty means the
+          // file genuinely has no text changes.
+          const other = await api.gitDiff(scope, diff.path, !diff.staged)
+          if (other.diff !== '') result = other
+        }
+        if (result.diff !== '') {
+          if (!cancelled) setData({ diff: result.diff })
+          return
+        }
+        // Empty diff: an untracked file (git diff never lists it) falls back
+        // to a full-file addition; anything else is a genuine no-text-change.
+        if (diff.untracked === true && !diff.staged) {
+          const text = await api.fsRead(scope, diff.path)
+          if (!cancelled) {
+            setData(text.kind === 'text' ? { diff: '', untracked: text.content } : { diff: '' })
+          }
+          return
+        }
+        if (!cancelled) setData({ diff: '' })
+      } catch (reason) {
+        if (!cancelled) setError(reason instanceof Error ? reason.message : String(reason))
+      } finally {
+        if (!cancelled) setLoading(false)
+      }
+    }
+    void load()
+    return () => { cancelled = true }
+  }, [sessionId, cwd, diff, tick])
+
+  return (
+    <div className={css.gitDiffTab}>
+      <div className={css.gitDiffTabHeader}>
+        <span className={css.gitDiffTabTitle} title={diff.kind === 'worktree' ? diff.path : `${diff.hash} ${diff.subject}`}>
+          {diff.kind === 'worktree' ? diff.path : `${diff.hash} ${diff.subject}`}
+        </span>
+        <button
+          type="button"
+          className={css.iconButton}
+          aria-label={t('refresh')}
+          title={t('refresh')}
+          onClick={refresh}
+        >
+          <IconRefreshOutline16 />
+        </button>
+      </div>
+      {loading && <div className={css.gitPlaceholder}>{t('loading')}</div>}
+      {!loading && error !== null && <div className={css.gitError}>{t('diffLoadError')}: {error}</div>}
+      {!loading && error === null && data !== null && (
+        <>
+          {data.untracked !== undefined
+            ? <DiffView diff="" untrackedPath={diff.kind === 'worktree' ? diff.path : ''} untrackedContent={data.untracked} />
+            : <DiffView diff={data.diff} />}
+          {data.diff === '' && data.untracked === undefined && (
+            <div className={css.gitEmpty}>{t('diffEmpty')}</div>
+          )}
+        </>
+      )}
+    </div>
+  )
+}