feat(gui): add native workspace folder picker

packages/client/runtime/tests/fake-api.ts

@@ -69,6 +69,8 @@ export class FakeApiClient implements IApiClient {
   onCancel: (payload: unknown) => Promise<RpcResponse<{ accepted: true }>> = () => Promise.resolve(ok({ accepted: true as const }))
   onDescribe: (payload: unknown) => Promise<RpcResponse<{ version: string; cwd: string; attachedSessions: number }>> =
     () => Promise.resolve(ok({ version: '0-fake', cwd: '/f', attachedSessions: 0 }))
+  onPickDirectory: (payload: unknown) => Promise<RpcResponse<{ path: string | null }>> =
+    () => Promise.resolve(ok({ path: null }))
 
   private readonly muxConns: StreamConn<MuxFrame>[] = []
   private readonly hostConns: StreamConn<HostFrame>[] = []
@@ -87,6 +89,7 @@ export class FakeApiClient implements IApiClient {
 
   readonly host: IApiClient['host'] = {
     describe: (payload: unknown) => this.record('host.describe', payload, this.onDescribe(payload)),
+    pickDirectory: (payload: unknown) => this.record('host.pickDirectory', payload, this.onPickDirectory(payload)),
   }
 
   onWorkspaceList: (payload: unknown) => Promise<RpcResponse<{ items: never[] }>> = () => Promise.resolve(ok({ items: [] }))