feat(setup): first-run wizard — admin, GitHub App, tunnel, done (#71)

* feat(setup): first-run wizard — admin, GitHub App, tunnel, done

- GET /api/v1/setup/status (public): has_users, needs_setup,
  has_github_app, has_tunnel. app_settings.setup_completed flag; installs
  with existing projects auto-complete so upgrades never see the wizard.
- POST /api/v1/setup/complete records the flag.
- /setup page: progress rail + four steps — create admin (links into the
  bootstrap sign-up with redirect back), GitHub App manifest flow,
  optional Cloudflare tunnel token, finish. Every optional step is
  skippable; nothing blocks.
- PlatformShell redirects signed-in users to /setup while needs_setup.
- The GitHub App callback honors a sessionStorage return marker set by
  the wizard so provisioning resumes at /setup instead of /settings.
- OpenAPI documents both endpoints.

Verified live: status reports auto-completed on this install,
complete persists the flag, response shape matches the client.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* test(setup): wizard step-state coverage

Five cases across the state machine: fresh-install account prompt,
sign-in resume, git-provider step, tunnel step, and finish.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/features/secondary/pages.tsx

@@ -1253,7 +1253,11 @@ export function GitHubAppCallbackPage() {
     mutationFn: (appCode: string) => convertGitHubAppCode(appCode),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['github-app-status'] });
-      navigate('/settings', { replace: true });
+      // The setup wizard stashes a return marker before submitting the
+      // manifest form — resume there instead of the settings page.
+      const inSetup = sessionStorage.getItem('containr.setup_return') === '1';
+      sessionStorage.removeItem('containr.setup_return');
+      navigate(inSetup ? '/setup' : '/settings', { replace: true });
     },
   });
   const firedRef = useRef(false);