B-7: Admin analytics aggregation endpoints

[KuchiMercy]

Summary

The admin panel needs data to power the analytics dashboard (F-10). Backend aggregation endpoints are needed to efficiently compute platform-wide metrics without sending raw data to the frontend.

Requirements

• Add GET /admin/analytics/overview — summary stats:
  • Total escrows (by status), total volume (XLM), total platform fees collected
  • Active users (last 30 days), new users (last 30 days)
• Add GET /admin/analytics/volume?period=daily|weekly|monthly&from=&to= — time-series data:
  • Escrow count and total value per time bucket
• Add GET /admin/analytics/disputes — dispute metrics:
  • Total disputes, dispute rate (% of escrows), avg resolution time
  • Resolution outcome distribution (released/refunded/split)
• Add GET /admin/analytics/top-users?limit=10 — leaderboard:
  • Wallet address, escrow count, total volume, completion rate
• Use TypeORM query builder for efficient SQL aggregation (not loading all records into memory)
• Cache results with a TTL (5 minutes) to avoid expensive re-computation on every request
• All endpoints require admin role

Acceptance Criteria

• Overview endpoint returns accurate summary statistics
• Volume endpoint returns time-series data groupable by day/week/month
• Dispute endpoint returns rate and resolution metrics
• Top users endpoint returns ranked user list
• All endpoints are protected by the admin guard
• Queries use SQL aggregation (GROUP BY, COUNT, SUM) not in-memory computation
• Results are cached with 5-minute TTL
• Date range filtering works on the volume endpoint

Context

• Admin controller: apps/backend/src/modules/admin/admin.controller.ts
• Admin service: apps/backend/src/modules/admin/admin.service.ts
• Escrow entity: apps/backend/src/modules/escrow/entities/escrow.entity.ts
• Admin guard: apps/backend/src/modules/auth/middleware/admin.guard.ts

Rollout Phase

Phase 5 — Admin & Production Hardening

Points: 150 (Medium)