fix: batch 4 — connection pooling, graceful shutdown, email verification UX

- Prisma: connection_limit=10, pool_timeout=30 on DATABASE_URL in both compose files
- Graceful shutdown: SIGTERM/SIGINT forwarded to Node process in docker-entrypoint.sh
- testEmailConnection: replaced real email send with transporter.verify(), simplified UI to single button
- NotificationLog.userId index: confirmed already present, no change needed

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -23,7 +23,7 @@ services:
       - .env
     environment:
       - NODE_ENV=production
-      - DATABASE_URL=postgresql://mopc:${DB_PASSWORD}@postgres:5432/mopc
+      - DATABASE_URL=postgresql://mopc:${DB_PASSWORD}@postgres:5432/mopc?connection_limit=10&pool_timeout=30
       - NEXTAUTH_URL=${NEXTAUTH_URL}
       - NEXTAUTH_SECRET=${NEXTAUTH_SECRET}
       - AUTH_SECRET=${NEXTAUTH_SECRET}