feat(finalist): deadline reminder emails via cron

Add sendDueConfirmationReminders() to finalist-confirmation.ts: queries
PENDING confirmations with no reminderSentAt whose deadline is within the
per-program LIVE_FINAL round reminderHoursBeforeDeadline window (default 12h),
sends a FINALIST_REMINDER in-app notification (+ email via pipeline) to the
team LEAD, then stamps reminderSentAt for idempotency.

Wire into the finalist-confirmations cron route alongside expirePendingPastDeadline.
Also clear reminderSentAt on re-invite in resetOrCreatePendingConfirmation so
re-invited teams get a fresh reminder window.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/api/cron/finalist-confirmations/route.ts

@@ -1,6 +1,9 @@
 import { NextResponse, type NextRequest } from 'next/server'
 import { prisma } from '@/lib/prisma'
-import { expirePendingPastDeadline } from '@/server/services/finalist-confirmation'
+import {
+  expirePendingPastDeadline,
+  sendDueConfirmationReminders,
+} from '@/server/services/finalist-confirmation'
 
 export async function GET(request: NextRequest): Promise<NextResponse> {
   const cronSecret = request.headers.get('x-cron-secret')
@@ -8,8 +11,11 @@ export async function GET(request: NextRequest): Promise<NextResponse> {
     return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
   }
   try {
-    const result = await expirePendingPastDeadline(prisma)
-    return NextResponse.json({ ok: true, ...result })
+    const [expireResult, reminderResult] = await Promise.all([
+      expirePendingPastDeadline(prisma),
+      sendDueConfirmationReminders(prisma),
+    ])
+    return NextResponse.json({ ok: true, ...expireResult, ...reminderResult })
   } catch (error) {
     console.error('[Cron] finalist-confirmations failed:', error)
     return NextResponse.json({ error: 'Internal error' }, { status: 500 })