Closing a signup is one-way; need a Reopen affordance

[richshaw]

Context

Today, closing a signup is a one-way door. The status machine in src/services/signups.ts allows draft → open (publish) and open → closed (close), but there's no closed → open transition. An organizer who accidentally closes a signup, or who closes one early but later wants to extend it, has no recovery — their only option is to archive it and start over.

The detail header now exposes Close while the signup is open (#19), but a closed signup shows no action at all besides Preview / Export. The status pill says closed and that's the end of it.

Proposed approach

Add a reopenSignup service + API + header button that mirrors the close path:

• Service (src/services/signups.ts): new reopenSignup(db, actor, id) delegating to transitionStatus(db, actor, id, 'closed', 'open', 'signup.reopened'). Add signup.reopened as an activity event kind.
• API (src/app/api/signups/[id]/reopen/route.ts): POST handler matching …/close/route.ts.
• Action (src/app/app/(chrome)/signups/[id]/actions.ts): reopenAction(signupId) analogous to closeAction.
• UI (src/components/signup/SignupHeader.tsx): when status === 'closed', render a Reopen button next to Preview/Export — same brand-fill styling as Publish/Close, mutually exclusive with both.

Status machine after this change:

• draft → open (publish)
• open ↔ closed (close / reopen)
• any → archived (terminal — still one-way, intentionally)

archived stays terminal because it implies the organizer is done; reopening from archive is out of scope.

Open questions

• Reminder jobs on reopen: closing a signup doesn't currently cancel pending reminders (worth confirming) — does reopen need to re-schedule anything, or does the existing singletonKey: commitmentId job model handle it?
• Public page caching: /s/[slug] renders different copy for closed vs open — confirm the existing layout revalidation in revalidateSignup is sufficient (it should be, since close already relies on it).
• Confirmation prompt: close currently has no confirm step. Reopen probably doesn't need one either, but worth a thought — accidental reopen is much less destructive than accidental close.

Tests

• Unit: extend the status-transition tests in src/services/*.test.ts to cover the new edge.
• DB: add a closed → open → closed round-trip in src/services/*.db.test.ts to confirm activity log entries land correctly.