Fix intermittent blank page and profile setup redirect loop

[nbudin]

Summary

• Blank page on initial load: RouterProvider (from react-router) initializes its state via useState(router.state). When the root route is lazy, the router starts with initialized=false/renderFallback=true, causing _renderMatches to return null — an empty container. RouterProvider then escapes that null state via startTransition, but something in the concurrent route tree keeps the transition suspended long enough to produce a blank screen lasting 25+ seconds. Fix: gate RouterProvider's mount on router.state.initialized. DataModeApplicationEntry subscribes to the router and shows a spinner until initialization completes, then mounts RouterProvider with an already-initialized state.

• Redirect loop after new user profile setup: Two bugs conspired to keep users stuck on /my_profile/setup after completing login: (1) UpdateUserConProfile mutation did not return needs_update in its selection set, so Apollo never wrote needs_update: false to the normalized cache after auto-save — every client-side navigation read stale needs_update: true and redirected back; (2) the "Finish" button on the setup form was a plain <Link>, so if the user changed nothing, UpdateUserConProfile was never called at all. Fixed by adding needs_update to the mutation response and changing the Finish button to fetcher.submit with a _redirectTo field so the action runs the mutation and redirects on success.

Test plan

• Load the app as a logged-out user — no blank screen on initial load
• Load the app as a returning user — no blank screen on initial load
• Log in as a new user (no convention profile) — should redirect to /my_profile/setup
• On /my_profile/setup, click "Finish" without changing anything — should navigate to / without redirecting back
• On /my_profile/setup, change a field (auto-save fires), then click "Finish" — should navigate to / without redirecting back
• After completing setup, navigate freely around the convention site — no redirect loops

🤖 Generated with Claude Code

[github-actions]

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
Overall Coverage	🟢 54.31%	🟢 54.31%	⚪ 0%

Minimum allowed coverage is 0%, this run produced 54.31%