feat(cli): add admin REPL + commands and docs

- Add CLI entry in backend with default REPL, persistent history, aliases
- Add commands: users:list/create/verify, events:list/details/participants/checkin,
  matches:list, logs:app, logs:messages
- Support running subcommands inside REPL via .cli and run()
- Add Makefile targets: dev-cli, prod-cli, dev/prod up/down (+rebuild)
- Update README and add docs/ADMIN_CLI.md
- Add CLI tests with mocked Prisma

README.md

@@ -364,6 +364,30 @@ Adds:
     - Click on another user's username
     - View profile: avatar, location, social media, statistics
 
+## 🧰 Admin CLI
+
+Use an in-container admin console for quick maintenance.
+
+- Start REPL (default): `docker compose exec backend npm run cli`
+- Explicit REPL: `docker compose exec backend npm run cli -- repl`
+- List users: `docker compose exec backend npm run cli -- users:list --limit 20`
+- Create user: `docker compose exec backend npm run cli -- users:create --email admin@example.com --username admin --password 'Secret123!'`
+- Verify email: `docker compose exec backend npm run cli -- users:verify --email admin@example.com`
+- List events: `docker compose exec backend npm run cli -- events:list --limit 10`
+- Event details by slug: `docker compose exec backend npm run cli -- events:details --slug warsaw-dance-2025 [--participants 25]`
+- Event participants: `docker compose exec backend npm run cli -- events:participants --slug warsaw-dance-2025 --limit 100`
+- Event participants CSV: `docker compose exec backend npm run cli -- events:participants --slug warsaw-dance-2025 --limit 200 --csv > participants.csv`
+- List matches: `docker compose exec backend npm run cli -- matches:list --limit 20 [--status accepted|pending|completed]`
+- Check-in user to event (simulate QR): `docker compose exec backend npm run cli -- events:checkin --username john_doe --slug warsaw-dance-2025`
+- App logs (if LOG_FILE configured): `docker compose exec backend npm run cli -- logs:app --lines 200`
+- Recent chat messages: `docker compose exec backend npm run cli -- logs:messages --limit 50`
+
+Production equivalents use `backend-prod` instead of `backend`.
+
+REPL specifics:
+- Inside REPL use `run('users:list --limit 20')` or `.cli users:list --limit 20`.
+- Top-level await works for Prisma: `await prisma.user.findMany({ take: 5 })`.
+
 ## 🔐 Security
 
 ### Implemented Security Features:
@@ -509,6 +533,7 @@ docker compose exec backend npm run test:coverage
 - `docs/PHASE_1.5.md` - Phase 1.5 documentation (Email & WSDC)
 - `docs/SECURITY_AUDIT.md` - Security audit & fixes
 - `docs/DEPLOYMENT.md` - Deployment guide
+- `docs/ADMIN_CLI.md` - Admin CLI & REPL usage
 - `docs/COMPLETED.md` - Completed tasks archive
 - `docs/RESOURCES.md` - Links to documentation and learning resources