feat(sidebar): 文件页与文件变动页 UIUX 重构 + 全局组件抽取

文件页（FileTree/TreePanel）
- Ctrl/Cmd 多选 + Shift 按可见行序连选（Esc/点空白/右键收敛），批量条支持复制路径、批量删除（共享 ConfirmDialog + 顺序 fsRemove）
- Git 变更着色：行名按状态上色 + M/A/D/U 徽标，目录按 dirHasChanges 着色，非仓库静默降级（数据来自共享 git 状态存储）
- 新建文件夹：fs.mkdir 路由 + mkdirWorkspaceEntry + 内联输入行（Enter/Esc/blur/IME 守卫）
- 性能：FileRow/DirRow memo（含反向验证）、搜索 hidden 停车不再卸载树、level 拉取世代守卫 + AbortController、fs.tree truncated 提示、use-dir-watch 入参 memo
- 拖拽上传视觉 token 化（硬编码色清零）；可见性下传后隐藏页签停止轮询
- 右键「打开方式」改为复用 DSH 自带 open-in-app（宿主探测的关联应用 + 文件管理器显示）

文件变动页（changes/diff）
- 36px 头（宿主 SegmentedControl）+ 单一 ChangeRow + SectionHeader 分组 + 吸底提交条单状态行 + 历史独立空态
- 修掉：双份空态、暂存失败 unhandled rejection、手动刷新被丢、仓库切换刷新两次、worktree 清单缺 repoRoot、工作树被自动切走、预览持旧快照、恢复高度未 clamp、session ops 无谓轮询
- DiffPane/DiffTab 共用 use-git-diff；修掉 DiffPane 的 untracked 预览从不渲染

全局组件与宿主接入
- 新增 src/client/ui（IconButton/Chip/SectionHeader/Notice/ConfirmDialog/StatusBadge + 共享 git 状态存储）
- 新增 src/client/open-in-app.ts（宿主 open-in-app 客户端适配），删除自研 open-with 全链路与 open.external 路由
- 客户端 inject 补 remote / remote.session：缺声明时 ctx.get('remote').session 会抛出并把整个面板打成错误条（真实挂载 lane 抓到）
- 词典：+25 键 / -20 openWith* / -noChanges，20 份同步

验证：typecheck / lint / test（126 文件 1322 通过）/ build 全绿；
DSH_CMD='npx -y --package @deepseek-ai/dsh@0.1.7-rc.1 dsh' pnpm test:mount 7/7 通过（含 tab sweep 与 perf lane）

src/client/DiffTab.tsx

@@ -5,157 +5,24 @@
  * 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 changes tab's staging/discard operations change the
- * very content it shows. Rendering goes through the shared {@link DiffFiles}
- * renderer — the same one the changes tab's inline preview uses.
+ * very content it shows. Loading IS the shared `useGitDiffTarget` hook (the
+ * changes tab's inline preview runs the same one, so the staged-side and
+ * untracked fallbacks and the per-file fold cache cannot drift apart);
+ * rendering goes through the shared {@link DiffFiles} renderer.
  */
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { useMemo } from 'react'
 import { IconRefreshOutlineRegular } 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 { DiffFiles } from './diff/DiffFiles.tsx'
-import { displayPath, foldRowsFromContents, type DiffFile, type DiffRow, type FoldSegment } from './diff/rows.ts'
+import { useGitDiffTarget } from './diff/use-git-diff.ts'
 import { t } from './locales.ts'
-import { resolveSidebarPath } from './paths.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)
-  // The staged flag of the side ACTUALLY rendered: when the requested side's
-  // diff came back empty the load falls back to the other side, and the fold
-  // expansion must read that side's revisions (else the sliced line numbers
-  // land on the wrong contents).
-  const [effectiveStaged, setEffectiveStaged] = useState<boolean | null>(null)
-
-  const refresh = useCallback((): void => { setTick(value => value + 1) }, [])
-
-  useEffect(() => {
-    let cancelled = false
-    const scope: SessionScope = { sessionId, cwd, ...(diff.repoRoot !== undefined ? { repoRoot: diff.repoRoot } : {}) }
-    setLoading(true)
-    setError(null)
-    setData(null)
-    setEffectiveStaged(null)
-    const load = async (): Promise<void> => {
-      try {
-        if (diff.kind === 'commit') {
-          const result = await api.gitCommitDiff(scope, diff.hashFull, diff.worktree)
-          if (!cancelled) setData({ diff: result.diff })
-          return
-        }
-        let result = await api.gitDiff(scope, diff.path, diff.staged, diff.worktree)
-        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, diff.worktree)
-          if (other.diff !== '') {
-            result = other
-            if (!cancelled) setEffectiveStaged(!diff.staged)
-          }
-        }
-        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) {
-          // A child-repo path is relative to diff.repoRoot, not the session
-          // cwd or the linked-worktree root; resolve against whichever the
-          // diff ref carries so the untracked fallback reads the right file.
-          const text = await api.fsRead(scope, resolveSidebarPath(diff.repoRoot ?? diff.worktree ?? cwd, 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])
-
-  // ── On-demand git fold expansion: a fold's hidden rows come from both
-  //    sides' full contents (git.show / fsRead), fetched ONCE per file so
-  //    sibling folds share the request, then sliced by each fold's line
-  //    ranges. The cache dies with the ref or a refresh tick. ──────────────
-  const foldContents = useRef(new Map<string, Promise<{ old: string; new: string }>>())
-  useEffect(() => { foldContents.current = new Map() }, [diff, tick])
-  const foldLoader = useMemo(() => {
-    const sidesOf = (file: DiffFile): Promise<{ old: string; new: string }> => {
-      // Both sides empty cannot cover a non-empty fold — treat it as a failed
-      // fetch so the fold degrades to the unavailable marker instead of
-      // silently expanding to nothing (the symptom of a bad rev or path
-      // reading null on both sides).
-      const ofSides = (oldContent: string | null, newContent: string | null): { old: string; new: string } => {
-        if ((oldContent ?? '') === '' && (newContent ?? '') === '') throw new Error('no content on either side')
-        return { old: oldContent ?? '', new: newContent ?? '' }
-      }
-      const fetchSides = async (): Promise<{ old: string; new: string }> => {
-        const scope: SessionScope = { sessionId, cwd, ...(diff.repoRoot !== undefined ? { repoRoot: diff.repoRoot } : {}) }
-        if (diff.kind === 'commit') {
-          // The patch's -m --first-parent shape: old side from the parent,
-          // new side from the commit (a root commit's parent read fails → '').
-          const [oldSide, newSide] = await Promise.all([
-            file.oldPath === '/dev/null'
-              ? Promise.resolve({ content: null })
-              : api.gitShow(scope, `${diff.hashFull}^`, displayPath(file.oldPath), diff.worktree),
-            file.newPath === '/dev/null'
-              ? Promise.resolve({ content: null })
-              : api.gitShow(scope, diff.hashFull, displayPath(file.newPath), diff.worktree),
-          ])
-          return ofSides(oldSide.content, newSide.content)
-        }
-        // Worktree change: staged is HEAD vs index, unstaged is index vs
-        // worktree (the worktree side reads the live file).
-        const staged = effectiveStaged ?? diff.staged
-        if (staged) {
-          const [oldSide, newSide] = await Promise.all([
-            file.oldPath === '/dev/null'
-              ? Promise.resolve({ content: null })
-              : api.gitShow(scope, 'HEAD', displayPath(file.oldPath), diff.worktree),
-            file.newPath === '/dev/null'
-              ? Promise.resolve({ content: null })
-              : api.gitShow(scope, ':0', displayPath(file.newPath), diff.worktree),
-          ])
-          return ofSides(oldSide.content, newSide.content)
-        }
-        const [oldSide, worktree] = await Promise.all([
-          file.oldPath === '/dev/null'
-            ? Promise.resolve({ content: null })
-            : api.gitShow(scope, ':0', displayPath(file.oldPath), diff.worktree),
-          api.fsRead(scope, resolveSidebarPath(diff.repoRoot ?? diff.worktree ?? cwd, displayPath(file.newPath))).catch(() => null),
-        ])
-        return ofSides(oldSide.content, worktree !== null && worktree.kind === 'text' ? worktree.content : null)
-      }
-      const path = displayPath(file.newPath === '/dev/null' ? file.oldPath : file.newPath)
-      let promise = foldContents.current.get(path)
-      if (promise === undefined) {
-        promise = fetchSides()
-        foldContents.current.set(path, promise)
-      }
-      return promise
-    }
-    return (file: DiffFile, segment: FoldSegment): Promise<readonly DiffRow[]> =>
-      sidesOf(file).then(sides => foldRowsFromContents(segment, sides.old, sides.new))
-  }, [sessionId, cwd, diff, effectiveStaged])
+  const scope = useMemo<SessionScope>(() => ({ sessionId, cwd }), [sessionId, cwd])
+  const { loading, error, diffText, untracked, refresh, resolveFold } = useGitDiffTarget(diff, scope)
 
   return (
     <div className={css.gitDiffTab}>
@@ -175,12 +42,12 @@ export function DiffTab(props: { sessionId: string; cwd: string | undefined; dif
       </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 && (
+      {!loading && error === null && diffText !== null && (
         <>
-          {data.untracked !== undefined
-            ? <DiffFiles diff="" untrackedPath={diff.kind === 'worktree' ? diff.path : ''} untrackedContent={data.untracked} />
-            : <DiffFiles diff={data.diff} resolveFold={foldLoader} />}
-          {data.diff === '' && data.untracked === undefined && (
+          {untracked !== undefined
+            ? <DiffFiles diff="" untrackedPath={diff.kind === 'worktree' ? diff.path : ''} untrackedContent={untracked} />
+            : <DiffFiles diff={diffText} resolveFold={resolveFold} />}
+          {diffText === '' && untracked === undefined && (
             <div className={css.gitEmpty}>{t('diffEmpty')}</div>
           )}
         </>