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.dev.yml

@@ -68,7 +68,7 @@ services:
     env_file:
       - ../.env
     environment:
-      - DATABASE_URL=postgresql://${POSTGRES_USER:-mopc}:${POSTGRES_PASSWORD:-devpassword}@postgres:5432/${POSTGRES_DB:-mopc}
+      - DATABASE_URL=postgresql://${POSTGRES_USER:-mopc}:${POSTGRES_PASSWORD:-devpassword}@postgres:5432/${POSTGRES_DB:-mopc}?connection_limit=10&pool_timeout=30
       - NEXTAUTH_URL=${NEXTAUTH_URL:-http://localhost:3000}
       - NEXTAUTH_SECRET=${NEXTAUTH_SECRET:-dev-secret-key-for-local-development-only}
       - AUTH_SECRET=${AUTH_SECRET:-dev-secret-key-for-local-development-only}