feat(host): adaptive directory-picker default via -auto chooser

Add @deepseek-ai/dsh-host-directory-picker-auto, a node-half-only chooser
that samples the host situation once at boot (bind host via a new
httpServer.host getter, SSH markers, platform, DISPLAY/WAYLAND_DISPLAY)
and mounts the matching dual-face backend (-native or -browse) as a real
Loader entry in the in-memory root tree; the effect disposer removes it.
Entry-level mounting keeps the seam's one-row-swaps-both-faces invariant:
the client module table discovers the mounted backend's browser half
exactly as a config row's. apps/cli now composes -auto as its
directory-picker row; composing a backend row directly remains the pin.

packages/host/README.zh.md

@@ -11,5 +11,6 @@ dsh web GUI 的宿主侧：所有客户端形态共用的 API 网关，以及承
 | `directory-picker/` | 工作区目录选择 seam：网关的 picker RPC 委托的可辨识 `native`／`browse` 能力 | `ctx.directoryPicker` |
 | `directory-picker-native/` | 双面原生交互：OS 选择器后端（osascript／PowerShell／Zenity+KDialog，仅宿主屏幕可用）+ 填入 ui-workspace 目录流 slot 的 browser half | （注册 `ctx.directoryPicker`） |
 | `directory-picker-browse/` | 双面浏览交互：基于 Node 标准库的列举／创建原语（可远程）+ 渲染应用内选择工作区目录对话框的 browser half | （注册 `ctx.directoryPicker`） |
+| `directory-picker-auto/` | 自适应选择器：启动时一次性判定宿主处境（绑定宿主、SSH、显示），并把匹配的双面后端挂载为内存中的 Loader 条目 | （挂载一个后端行） |
 
 `apiproxy` 在设计上与传输方式无关——它不注册任何路由；载体自行包装 `ctx.apiProxy`。HTTP 载体路由（连同其 `/api` 浏览器信任栅栏）由 [`client/connection`](../client/connection/README.md) 的 node 半侧挂载，这正是该包住在 client 组的原因：它拥有这条线的两端。