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

ledger/models.py

@@ -36,6 +36,7 @@ class RazorpayTransaction(models.Model):
     status = models.CharField(
         max_length=50,
         help_text="created/authorized/captured/failed/refunded",
+        db_index=True,
     )
     method = models.CharField(
         max_length=50,
@@ -59,7 +60,7 @@ class RazorpayTransaction(models.Model):
     # Timestamps
     created_at = models.DateTimeField(auto_now_add=True)
     updated_at = models.DateTimeField(auto_now=True)
-    captured_at = models.DateTimeField(blank=True, null=True)
+    captured_at = models.DateTimeField(blank=True, null=True, db_index=True)
 
     def __str__(self):
         return f"{self.razorpay_payment_id or self.razorpay_order_id} - {self.status}"