feat(admin): recruitment console (PR A of 3)

[ishanshaurya]

Admin console for the recruitment drive — open/close it and set the Google
Form /join embeds, no redeploy needed. Depends on #203 (merged) — already
rebased onto main.

What's here

• PATCH /api/admin/recruitment — admin-gated, backed by updateRecruitmentSettings()
• /admin/recruitment page + RecruitmentPanel — mirrors admin/users + UserManagementPanel
• admin/layout.tsx + AdminNav — shared nav, extracted from the duplicated blocks in
  admin/page.tsx and admin/users/page.tsx. Visible side effect: admin/teachers,
  admin/problems/new, and admin/problems/[slug]/edit now show this nav too (they had
  none, or in teachers' case were missing it).

The layout is presentational only — every page keeps its own getAdminUser() +
redirect("/") and its own export const dynamic = "force-dynamic"; the route handler
is gated independently of the page.

Verified

• npm run test / tsc --noEmit / lint / build all clean
• Manually in-browser: nav consistent across all 5 admin pages, URL save + reload
  persistence, bad-URL rejected with inline error and no write, partial save (toggle
  alone) doesn't clobber the URL field, gate bounces both signed-out and signed-in
  non-admin users to /

[vercel]

@ishanshaurya is attempting to deploy a commit to the barunaniket-9400's projects Team on Vercel.

A member of the Team first needs to authorize it.

[barunaniket]

Approving. The part that mattered most here is right, and it's the part that was easiest to get wrong.

Security review of the nav extraction

The risk in this PR was the layout swallowing the auth gate. It doesn't:

• All six /admin/* pages keep their own getAdminUser() + redirect("/") and their own export const dynamic = "force-dynamic". Verified individually, including the three that only inherit the nav (teachers, problems/new, problems/[slug]/edit) — the diff removed markup and nothing else.
• PATCH /api/admin/recruitment gates independently of the page, which is what matters for a handler reachable by direct POST.
• The comment in layout.tsx explaining why the layout can't be the boundary is the right thing to leave behind for whoever touches this next.

Things you did that weren't asked for and should stay

• The panel sends only changed fields. Two admins in two tabs won't silently overwrite each other's untouched values. The comment explaining it is accurate.
• Syncing state from the server's persisted response instead of echoing the request. Correct for updatedAt/updatedBy and for any server-side normalization.
• Disabling Save when !dirty, and keeping the form dirty after a failed save so a retry is possible.

Checked and deliberately not flagged

No enforceRateLimits on the new route — but no existing route under src/app/api/admin/** uses it either, so this matches the codebase rather than deviating from it. Fine as is.

Cosmetic, not blocking — I'll take these in a follow-up

1. Double top padding on the three inherited pages. admin/page.tsx and admin/users/page.tsx had pt-6 dropped from their section (correctly, since the layout now supplies it), but teachers, problems/new and problems/[slug]/edit still carry pt-6 — so those three get the gap twice.
2. Nav width mismatch on the problem pages. The layout wrapper is max-w-4xl; problems/new and problems/[slug]/edit are max-w-3xl, so the nav sits wider than the content it heads.

Neither is worth another round trip on your branch — merging this and fixing both in a follow-up.

Optional, from the plan, if you'd rather pick them up than have me: a preview link that opens the saved form in a new tab (so an admin can confirm the paste before opening the drive), and a plain-language status line — "Recruitment is open. /join is showing the form."