Expose a /api/health Endpoint That Reports Live Status of the Database, Redis, and Stellar Dependencies

[mftee]

Description:
Expose a standalone /api/health endpoint using @nestjs/terminus that reports the live status of all critical dependencies (database, Redis, Stellar).

Tasks:

• Install @nestjs/terminus
• Create src/health/health.module.ts and health.controller.ts
• Add checks: TypeOrmHealthIndicator (database), HttpHealthIndicator (Stellar Horizon URL), a custom RedisHealthIndicator
• Return 200 OK with a status summary when all checks pass; 503 Service Unavailable when any check fails
• The endpoint should be publicly accessible (no auth guard)

Acceptance Criteria:

• GET /api/health returns a JSON body listing the status of each dependency
• A failing database connection causes the endpoint to return 503
• The endpoint is excluded from rate limiting