fix(client,host): review round — hooks-compartment occupancy, StrictMode re-arm, internal flow module, honest swap comment

- Directory-flow occupancy moves onto the inject face's reserved hooks
  compartment: apply publishes a stable observable per surface and the
  renderer binds useDirectoryFlow — no hand-rolled component subscriptions
  (the client contract's channel for registrant-private reactive facts).
- The native flow's alive guard re-arms in effect setup: StrictMode's
  development replay ran the cleanup once and every later outcome was
  discarded.
- NativeDirectoryFlow moves to a package-internal module; ./client exports
  only the Loader surface, tests import the internal module directly.
- The composition swap comment no longer advertises -browse as a complete
  swap before its dialog lands (stacked follow-up).

packages/host/directory-picker-native/tests/client-flow.spec.tsx

@@ -5,7 +5,8 @@ import { act, cleanup, render } from '@testing-library/react'
 import { afterEach } from 'vitest'
 import { SlotsService } from '@deepseek-ai/dsh-client-runtime/client'
 import type { DirectoryFlowOwnerProps } from '@deepseek-ai/dsh-client-ui-workspace/client'
-import { apply, inject, NativeDirectoryFlow } from '../src/client/index.ts'
+import { apply, inject } from '../src/client/index.ts'
+import { NativeDirectoryFlow } from '../src/client/flow.ts'
 
 afterEach(cleanup)