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.md

@@ -11,5 +11,6 @@ The host side of the dsh web GUI: the API gateway every client shape shares, and
 | `directory-picker/` | Workspace-directory picking seam: discriminated `native`/`browse` capability the gateway's picker RPCs delegate to | `ctx.directoryPicker` |
 | `directory-picker-native/` | Dual-face native interaction: OS-chooser backend (osascript / PowerShell / Zenity+KDialog, host-display only) + the browser half filling ui-workspace's directory-flow slots | (registers `ctx.directoryPicker`) |
 | `directory-picker-browse/` | Dual-face browse interaction: listing/creation primitives over Node stdlib (remote-capable) + the browser half rendering the in-app Select Workspace Directory dialog | (registers `ctx.directoryPicker`) |
+| `directory-picker-auto/` | Adaptive chooser: resolves the host's situation once at boot (bind host, SSH, display) and mounts the matching dual-face backend as an in-memory Loader entry | (mounts a backend row) |
 
 `apiproxy` is transport-agnostic by design — it registers no routes; carriers wrap `ctx.apiProxy` themselves. The HTTP carrier route (with its `/api` browser-trust fence) is mounted by [`client/connection`](../client/connection/README.md)'s node half, which is why that package lives in the client group: it owns both ends of the wire.