fix(host,client): default-export the picker seam; invalidate stale kind reads

ds-review-bot round 3. The seam package broke the service-package export
contract (named export only), so the config catalog filed it under Other
libraries and default imports failed; it now default-exports DirectoryPicker
like every abstract seam, and the regenerated catalog lists it as one.

The picker-kind effect also let a settlement from a superseded flow open
leak into the current one (close/reopen mid-describe, or a reconnect that
swaps the backend): the read now resets the affordance on every open and a
cleanup-toggled flag discards obsolete settlements, both directions pinned
by jsdom races.

packages/host/directory-picker/src/index.ts

@@ -128,3 +128,5 @@ export abstract class DirectoryPicker extends Service {
    */
   abstract capability(): DirectoryPickerCapability
 }
+
+export default DirectoryPicker