feat: Phase 1+2 - JWT auth, dashboard metrics API, DB indexes

Phase 1 - JWT Auth Foundation:
- Replace token auth with djangorestframework-simplejwt
- POST /api/v1/admin/auth/login/ - returns access + refresh JWT
- POST /api/v1/auth/refresh/ - JWT refresh
- GET /api/v1/auth/me/ - current admin profile
- GET /api/v1/health/ - DB health check
- Add ledger app to INSTALLED_APPS

Phase 2 - Dashboard Metrics API:
- GET /api/v1/dashboard/metrics/ - revenue, partners, events, tickets
- GET /api/v1/dashboard/revenue/ - 7-day revenue vs payouts chart data
- GET /api/v1/dashboard/activity/ - last 10 platform events feed
- GET /api/v1/dashboard/actions/ - KYC queue, flagged events, pending payouts

DB Indexes (dashboard query optimisation):
- RazorpayTransaction: status, captured_at
- Partner: status, kyc_compliance_status
- Event: event_status, start_date, created_date
- Booking: created_date
- PaymentTransaction: payment_type, payment_transaction_status, payment_transaction_date

Infra:
- Add Dockerfile for eventify-backend container
- Add simplejwt to requirements.txt
- All 4 dashboard views use IsAuthenticated permission class

requirements.txt

@@ -1,2 +1,3 @@
 Django>=4.2
 Pillow
+django-summernote