feat(native): render the plugin's tabs in DSH's native right Sidebar

Phase 2 of the 0.1.5 adaptation: the plugin stops drawing its own right
panel and contributes tab TYPES to DSH's native right Sidebar, which owns
the right column. The bottom workbench (terminal dock) stays plugin-owned.

Registrations (src/client/native/):
- every TabDescriptor becomes a native tab type (kind = descriptor.id, the
  default `extension` band) plus a keyed body in `sidebar.right.pane.tab`
  and a live chip title in `sidebar.right.pane.tab.title`
- the `editor` type also claims `dsh-resource://file/**`, so it outranks
  the built-in `text` preview (fallback) and every file the product opens
  lands in the plugin's editor
- the built-in `files` page kind is TAKEN OVER by an extension
  registration of the same kind: `openTab('files')` draws the plugin's
  explorer, and the built-in resumes when the plugin unregisters
- registrations follow the plugin registry + the side-card settings: a
  type registered later (external plugin) gets its native type too, a
  disabled type is unregistered (absent from the guide, refuses opens)

Adapter (src/client/native/tab-adapter.tsx):
- one synthetic plugin `SidebarTab` per native tab id, minted from the
  native record + navigation params (or the descriptor's own createTab,
  which a native guide open bypasses), kept live across navigations and
  updateTab writes
- the explorer's per-tab expansion/reveal sets and the per-kind instance
  counter, which the plugin's own layout used to hold

Service routing (src/client/service.ts):
- `setSurface` installs the native write face; openTab/openFile land
  natively (a path becomes a resource address, a path-less editor open
  becomes the `files` page, the rest carry the seed as navigation params),
  closeTab/updateTab/activateTab recognise native tab ids
- new optional `OpenTabSeed.target` ('right' default, 'bottom' keeps the
  bottom workbench); the bottom panel's own + menu and auto-terminal pass
  'bottom'
- src/client/native/surface.ts probes the controller's per-session writes
  (`openTabIn`/`openResourceIn`/`closeIn`, not in `ISidebarRight`) and
  queues opens for a session whose surface is not mounted yet

Right panel retired behaviourally (Phase 3 deletes the code): Sidebar
renders its bottom workbench only, keeps the panel collapsed, and hides
the right-panel toggle. The panel-specific e2e specs are removed; the
mount lane now drives the native guide (tab sweep), the plugin explorer
inside the native pane (editor/mermaid/README chunks) and the sidechat
host routes.

Verified: pnpm typecheck / lint / build / test (126 files, 1349 tests) /
check:consumer-types, plus pnpm test:mount against a real
@deepseek-ai/dsh@0.1.5-alpha.1 host (7/7).

docs/external-plugin-guide.md

@@ -8,6 +8,27 @@
 
 ---
 
+## 0. 承载面：DSH 原生右侧栏（v0.19.0-alpha.0 起）
+
+从 v0.19.0-alpha.0 起，插件**不再自绘右侧面板**：你的 tab 渲染在 **DSH 自己的右侧栏**里（`ctx.sidebarRight` / `ctx.sidebarRightTabs`），插件把每个 `TabDescriptor` 注册成原生 tab 类型（`kind = descriptor.id`）+ 一个原生 tab 体。对你的接入代码**没有影响**——仍然只调用 `ctx.betterSidebar`：
+
+- `registerTab` / `registerFileViewer` 签名不变；
+- `openTab` / `openFile` 默认落到原生右侧栏；新增可选 `OpenTabSeed.target`（`'right'` 默认 / `'bottom'` 落插件的底部工作台）；
+- `updateTab` / `closeTab` / `activateTab` 认识原生 tab id（插件为每个原生 tab 维护一条合成 `SidebarTab` 记录，`tab.meta` / `tab.path` 的写入照旧生效）。
+
+行为差异（写在这里以免踩坑）：
+
+| 事项 | 说明 |
+|---|---|
+| 生命周期回调 | 原生面只有「一次打开」，不区分新建/聚焦，因此只触发 `onOpen`（`onActivate` 仅在插件自己的底部工作台里触发） |
+| 去重 | 原生按 `(kind, 地址)` 去重：有 `createTab` 的类型每次新开一个 tab（terminal / browser / sidechat / diff），其余聚焦已有 tab；`dedupeKey` 的自定义语义不参与原生面 |
+| 布局持久化 | 原生栏的布局**只在内存**（刷新后回到折叠默认），插件自己的底部工作台仍然持久化 |
+| 跨会话打开 | 目标会话的右侧栏 store 未挂载时，打开会排队到该会话上屏后重放 |
+| 内置类型接管 | 插件的 `editor` 类型以 `extension` 优先级认领 `dsh-resource://file/**`（压过内置 `text` 预览），并接管内置 `files` 页面 kind（`openTab('files')` 打开插件的文件树）；插件卸载/禁用时内置实现自动复位 |
+| 终端上限 | 终端 tab 的数量上限只统计插件自己底部工作台里的终端；原生栏里的终端不计入 |
+
+---
+
 ## 1. 总览：你能扩展什么
 
 better-sidebar 从 v0.4.0 起把自己改造成一个**注册表服务**：