feat: add admin metrics endpoints with scheduled aggregation (#156)

[kalbliz]

Summary

• Adds admin-protected GET /api/v1/admin/metrics/tvl, /revenue, and /active-users endpoints returning { success, data, timestamp } envelopes
• Introduces MetricsModule with a 5-minute MetricsScheduler that aggregates TVL, cumulative protocol fees, and 24h/7d/30d active traders, caching results in Redis and persisting ProtocolMetricsSnapshot rows
• Adds AdminGuard (JWT + role: admin), Prisma schema extensions/migrations, and fixes the Soroban event indexer to upsert pools and use Pool.id for trade FKs
• Includes local dev improvements: Redis service in Docker Compose, express-rate-limit dependency, and small build fixes (logger types, Horizon fee lookup, compression import, etc.)

Test plan

• npx jest src/metrics/metrics.service.spec.ts src/auth/guards/admin.guard.spec.ts (9/9 passing)
• POST /api/v1/admin/login with ADMIN_PASSWORD returns JWT
• Unauthenticated GET /api/v1/admin/metrics/tvl returns 401
• Authenticated calls to all three metrics endpoints return success: true
• Verified Redis cache keys and protocol_metrics_snapshots rows are written by scheduler
• Run docker compose up -d db redis + npm run prisma:migrate on a fresh checkout
• Seed pools/trades and confirm non-zero TVL/revenue/active-user values after aggregation

Notes

• TVL depends on Pool.reserveA/B being populated; returns honest 0 until reserve sync lands
• Protocol revenue is derived from indexed swaps × pool fee bps, not on-chain treasury balance
• Active users count distinct swapper addresses in trades

Closes #156