feat(host,client): compose directory picking through slots — dual-face -native, no wire advertisement

ui-workspace's two trigger surfaces each declare a single-kind directory-flow
hole (conversation.hero.workspace.directoryFlow / sidebar.workspaces.directoryFlow,
same owner contract) and keep only the trigger and the adoption: the Open-local-
folder entry renders while the surface's hole is occupied, and the occupant
reports one picked path per open through the hole's owner conversation
(open/busy/onPicked/onCancel/onError).

directory-picker-native becomes dual-face: its browser half fills both holes
with a renderless occupant driving host.pickDirectory, so the cordis.yml row
that mounts the backend also composes the client interaction — a mismatch is
impossible and a second flow package fails at client load.

With composition wiring both sides, the host.describe.directoryPicker
advertisement and the client's kind branching lose their last consumer:
the field, WorkspacesService.directoryPickerKind(), the DirectoryPickerKind
wire type, and the picker's per-open describe read are deleted. The connection
fixture now serves a deterministic pickDirectory path so the keyless snapshot
drives the full pick-then-adopt flow. ui-workspace's hand-rolled declaration
deferral is replaced by the deferRegistration helper it duplicated.

pnpm-lock.yaml

@@ -2760,12 +2760,27 @@ importers:
         specifier: workspace:^
         version: link:../../util/native-command
     devDependencies:
+      '@deepseek-ai/dsh-client-runtime':
+        specifier: workspace:^
+        version: link:../../client/runtime
+      '@deepseek-ai/dsh-client-ui-slots':
+        specifier: workspace:^
+        version: link:../../client/ui-slots
+      '@deepseek-ai/dsh-client-ui-workspace':
+        specifier: workspace:^
+        version: link:../../client/ui-workspace
       '@deepseek-ai/dsh-invariants':
         specifier: workspace:^
         version: link:../../support/invariants
+      '@types/react':
+        specifier: ~18.3.1
+        version: 18.3.31
       cordis:
         specifier: ^4.0.0-rc.7
         version: 4.0.0-rc.7(@cordisjs/plugin-include@1.0.4)(@cordisjs/plugin-loader@1.0.0-rc.5)
+      react:
+        specifier: ^18.2.0
+        version: 18.3.1
 
   packages/host/webserver:
     dependencies: