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.

tsconfig.client.json

@@ -19,6 +19,8 @@
     "packages/client/*/src/css-modules.d.ts",
     "packages/client/*/tests/**/*.ts",
     "packages/client/*/tests/**/*.tsx",
+    "packages/host/directory-picker-native/tests/**/*.ts",
+    "packages/host/directory-picker-native/tests/**/*.tsx",
     "packages/client/tsdown.client.ts",
     "scripts/client-bundle-purity.spec.ts"
   ],
@@ -27,6 +29,10 @@
     // smoke policy). webserver has zero workspace deps and no cordis merge,
     // so it cannot drag host-side Context augmentation into this program.
     { "path": "./packages/host/webserver" },
+    // Dual-face host leaf: the node half is the native picking backend, the
+    // browser half registers the picking flow into ui-workspace's slot —
+    // client-side Context merges keep it out of the host program.
+    { "path": "./packages/host/directory-picker-native" },
     { "path": "./packages/client/ui-slots" },
     { "path": "./packages/client/ui-primitives" },
     { "path": "./packages/client/web-react" },