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/webserver/src/index.ts

@@ -78,6 +78,11 @@ export class HttpServerService extends Service {
     return this.listenedPort
   }
 
+  /** The configured bind host (the loopback or all-interfaces literal). */
+  get host(): Config['host'] {
+    return this.config.host
+  }
+
   /**
    * Register a named route. Duplicate (kind, path) throws — route patterns are
    * a composition-level contract, so a collision is a misconfiguration.