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/directory-picker-auto/tests/resolve.spec.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest'
+import { resolveDirectoryPickerBackend } from '../src/resolve.ts'
+import type { DirectoryPickerHostFacts } from '../src/resolve.ts'
+
+/** Baseline facts that resolve to `native`; each case overrides one signal. */
+const attended: DirectoryPickerHostFacts = {
+  bindHost: '127.0.0.1',
+  platform: 'darwin',
+  env: {},
+}
+
+describe('resolveDirectoryPickerBackend', () => {
+  it('resolves native for a loopback bind on a display platform', () => {
+    expect(resolveDirectoryPickerBackend(attended)).toBe('native')
+    expect(resolveDirectoryPickerBackend({ ...attended, platform: 'win32' })).toBe('native')
+  })
+
+  it('resolves browse for an all-interfaces bind regardless of other signals', () => {
+    expect(resolveDirectoryPickerBackend({ ...attended, bindHost: '0.0.0.0' })).toBe('browse')
+  })
+
+  it('resolves browse under an SSH launch (either env marker)', () => {
+    expect(resolveDirectoryPickerBackend({ ...attended, env: { SSH_CONNECTION: '10.0.0.2 55 10.0.0.9 22' } })).toBe('browse')
+    expect(resolveDirectoryPickerBackend({ ...attended, env: { SSH_TTY: '/dev/pts/3' } })).toBe('browse')
+  })
+
+  it('requires a display session on platforms without an implied one', () => {
+    expect(resolveDirectoryPickerBackend({ ...attended, platform: 'linux' })).toBe('browse')
+    expect(resolveDirectoryPickerBackend({ ...attended, platform: 'linux', env: { DISPLAY: ':0' } })).toBe('native')
+    expect(resolveDirectoryPickerBackend({ ...attended, platform: 'linux', env: { WAYLAND_DISPLAY: 'wayland-1' } })).toBe('native')
+  })
+
+  it('treats blank env exports as unset', () => {
+    expect(resolveDirectoryPickerBackend({ ...attended, env: { SSH_CONNECTION: '', SSH_TTY: '' } })).toBe('native')
+    expect(resolveDirectoryPickerBackend({ ...attended, platform: 'linux', env: { DISPLAY: '', WAYLAND_DISPLAY: '' } })).toBe('browse')
+  })
+})