feat(files): tree rename (inline) + delete (confirmed) + submenu visual tether

资源管理器补全：文件树右键菜单新增「重命名」（行内编辑：预填+全选、
Enter/失焦提交、Esc 取消、IME 组合键守卫）与「删除」（Modal 确认，文件/
目录文案区分，永久删除——宿主无回收站）。根行（工作区根）不提供两项，
服务端 fs.rename/fs.remove 双保险拒绝；目标已存在 409；link-aware——
symlink 行只改/删链接本身（lstat 判定），fence 校验对解析后目标进行。

落定收尾：pruneTree 清旧前缀缓存 + 收起 stale expanded + 单层重载父目录；
tab 调解走 service（rename→updateTab 改路径改标题、delete→closeTab 关
受影响 tab，覆盖两侧分栏/底栏/浮动窗口，经 tree-mutations.ts）。

二级菜单视觉关系（layout.css，仍限 data-dsh-sidebar-submenu 作用域）：
父行在子菜单打开期间保持高亮（宿主已渲染 aria-expanded="true"），
卡片间距 10px→4px（悬停走廊同步收窄），翻转规则一并 4px。

i18n 新增 7 key × 20 语言文件（locales.spec 的 key-set-parity 门禁）。
测试：fs-operations 追加 12 例（rename/remove 全失败面）；新增
file-tree-rename-delete.spec.tsx 8 例（菜单可见性/重命名流/删除流/错误条）；
menu-flip.spec.tsx 契约扩展覆盖 tether 规则。设计文档
docs/plans/2026-09-04-file-tree-rename-delete-design.md。

src/client/tree-mutations.ts

@@ -0,0 +1,50 @@
+/**
+ * Open-tab reconciliation after a file-tree mutation (rename/delete).
+ *
+ * The tree owns the rows; the TABS live in the sidebar state (either split
+ * tree, the bottom panel, or free windows). A rename must retarget every
+ * tab whose `path` is the renamed file (the editor content survives and
+ * later saves land on the new path); a delete must close every tab at or
+ * under the removed path — files and anything inside a removed directory
+ * (a stale tab's next save would fail against a missing path). Both ride
+ * the SERVICE paths (`updateTab`/`closeTab`) rather than direct state
+ * reducers so the registered lifecycle callbacks fire like any other tab
+ * mutation.
+ */
+import type { Context } from '../context-types.ts'
+import { baseName } from './FileTree.tsx'
+import { allLeaves, type SidebarSnapshot, type SidebarStore, type SidebarTab } from './state.ts'
+import { isWithinWorkspace } from './paths.ts'
+
+/** Every open tab that carries a file path (either split tree, the bottom
+ *  panel, and free windows — a floating tab is as open as a docked one). */
+function pathTabsOf(snapshot: SidebarSnapshot): SidebarTab[] {
+  const state = snapshot.state
+  if (state === undefined) return []
+  const tabs: SidebarTab[] = []
+  for (const leaf of allLeaves(state.splits)) tabs.push(...leaf.tabs)
+  for (const leaf of allLeaves(state.bottomSplits)) tabs.push(...leaf.tabs)
+  for (const float of state.floats) tabs.push(float.tab)
+  return tabs.filter(tab => tab.path !== undefined)
+}
+
+/** Retarget tabs after `oldPath` became `newPath` (title follows the new
+ *  base name, matching how openFile titles editor tabs). */
+export function retargetPathTabs(ctx: Context, store: SidebarStore, oldPath: string, newPath: string): void {
+  const service = ctx.get('betterSidebar')
+  if (service === undefined) return
+  for (const tab of pathTabsOf(store.getSnapshot())) {
+    if (tab.path === oldPath) service.updateTab(tab.id, { path: newPath, title: baseName(newPath) })
+  }
+}
+
+/** Close tabs at or under the removed `target` (a directory takes its whole
+ *  subtree of open files with it). */
+export function closePathTabs(ctx: Context, store: SidebarStore, target: string): void {
+  const service = ctx.get('betterSidebar')
+  if (service === undefined) return
+  for (const tab of pathTabsOf(store.getSnapshot())) {
+    const path = tab.path
+    if (path !== undefined && (path === target || isWithinWorkspace(target, path))) service.closeTab(tab.id)
+  }
+}