feat(ui): 自由窗口——tab 拖出侧边栏成为可移动/缩放/置顶的浮动窗口 (v0.16.0)

- 拖出：标签栏 tab 拖到主会话列（HTML5 DnD 检测 + 虚线提示浮层）或右键菜单
  「移动到自由窗口」（右/底面板共用 TabBar），tab 从 pane 移动进 SidebarState.floats
- 窗口（FreeWindow，渲染于 [data-dsh-panel-host] z-42）：头部 pointer 拖动
  （rAF 直写 + 松手提交）、拖到 pane 高亮停靠（center 合并）、SE 角缩放、
  点击置顶、头部右键（回到侧边栏/关闭）、X = closeTab 走正常生命周期
- 服务语义：openTab dedupe/id 聚焦浮动 tab = 置顶窗口（不展开面板）；
  closeTab/activateTab 兼顾 floats；agent 终端 reconcile 覆盖浮窗；
  features 单调新增 'floatWindows'，版本 0.16.0
- 持久化：floats 随会话 localStorage，sanitizeState 宽容校验 + 几何钳制，
  uid 播种覆盖 float 前缀；i18n 三键 19 语言同步
- 关键修复（e2e 发现）：portal 覆盖层（头部 Menu）的合成事件沿 React 树
  冒泡回拖拽表面，劫持菜单行点击——拖拽起点加 DOM 同源守卫（jsdom 不复现）
- e2e-mount.sh：缺省 tarball 改取 mtime 最新（旧字典序选择会把冒烟挂到
  过期产物）；新增 tests/e2e/float-window.e2e.ts 双用例

src/client/TabBar.tsx

@@ -4,8 +4,9 @@
  * button cluster, and the + menu that opens new tabs (explorer / git /
  * terminal). Tabs are draggable; dropping onto another tab inserts before it,
  * dropping on the strip background appends to this pane. Right-clicking a
- * tab opens the tab context menu (close / close others / close to the left /
- * close to the right, all scoped to this pane).
+ * tab opens the tab context menu (float as a free window / close / close
+ * others / close to the left / close to the right, the close ones scoped to
+ * this pane).
  */
 import { useEffect, useRef, useState, type ReactNode } from 'react'
 import clsx from 'clsx'
@@ -63,6 +64,9 @@ export function TabBar(props: {
   newTabOptions: NewTabOption[]
   /** Drop of a tab from any pane: (payload, insertBeforeTabId | null). */
   onDropTab: (payload: TabDragPayload, before: string | null) => void
+  /** Float a tab out as a free window (the tab context menu's entry; the
+   *  drag-to-conversation gesture is handled at the Sidebar shell level). */
+  onFloatTab: (tabId: string) => void
   /** Icon resolver for tab labels (reads from the tab descriptor registry). */
   getTabIcon?: (tab: SidebarTab) => ReactNode
   /** Badge resolver for tab labels (reads the descriptor's `badge`; the
@@ -70,7 +74,7 @@ export function TabBar(props: {
   getTabBadge?: (tab: SidebarTab) => ReactNode
 }) {
   const {
-    paneId, tabs, active, onActivate, onClose, onNewTab, newTabOptions, onDropTab, getTabIcon, getTabBadge,
+    paneId, tabs, active, onActivate, onClose, onNewTab, newTabOptions, onDropTab, onFloatTab, getTabIcon, getTabBadge,
   } = props
   const [menuOpen, setMenuOpen] = useState(false)
   // The tab right-click context menu: the target tab plus the cursor
@@ -271,6 +275,7 @@ export function TabBar(props: {
           open={tabMenu !== null && tabMenuIndex >= 0}
           onClose={() => { setTabMenu(null) }}
           items={[
+            { id: 'float', label: t('moveToFreeWindow') },
             { id: 'close', label: t('close') },
             { id: 'closeOthers', label: t('closeOtherTabs'), ...(tabs.length <= 1 ? { disabled: true } : {}) },
             { id: 'closeLeft', label: t('closeLeftTabs'), ...(tabMenuIndex <= 0 ? { disabled: true } : {}) },
@@ -282,7 +287,9 @@ export function TabBar(props: {
             setTabMenu(null)
             const index = tabs.findIndex(tab => tab.id === target.tabId)
             if (index < 0) return
-            if (id === 'close') {
+            if (id === 'float') {
+              onFloatTab(target.tabId)
+            } else if (id === 'close') {
               onClose(target.tabId)
             } else if (id === 'closeOthers') {
               for (const tab of tabs) {