frontend: add Create-profile setup screen for brand-new accounts

LoginGate now shows CreateProfile (display name only) instead of App when
an authenticated session has no provisioned geniusrun profile yet, backed
by the new POST /api/setup endpoint and session/me's has_profile flag.

frontend/src/api/client.ts

@@ -46,6 +46,11 @@ export const api = {
   // browser navigation. Logout must POST (see server.go's route), which an
   // <a href> can't do, hence the form.
   getSessionInfo: () => request<SessionInfo>("/api/session/me"),
+  setup: (displayName: string) =>
+    request<{ user_id: number; display_name: string }>("/api/setup", {
+      method: "POST",
+      body: JSON.stringify({ display_name: displayName }),
+    }),
 
   // Auth
   login: () => request<AuthResponse>("/api/auth/login", { method: "POST" }),