chore: add health check endpoint and structured logging to backend

[ryzen-xp]

📝 Description

Add a /health endpoint for uptime monitoring and configure structured JSON logging so backend logs are parseable in production. Both are necessary before any deployment.

✅ Requirements

• Install @nestjs/terminus and create HealthModule
• Implement GET /health that checks: HTTP server status, PostgreSQL connection, Stellar RPC reachability
• Each health indicator returns { status: 'up' | 'down', details?: object }
• Overall response is 200 when all healthy, 503 when any indicator is down
• Install nestjs-pino or winston for structured JSON logging
• Replace default NestJS logger with structured logger
• Every log line includes: timestamp, level, context (module name), message
• Log all incoming requests with method, path, statusCode, and response time
• Add LOG_LEVEL env var (default: info)

🎯 Acceptance Criteria

• GET /health returns correct status for all three indicators
• Returns 503 when database is unreachable
• All logs are valid JSON in production mode
• Request logs include method, path, status, and duration
• LOG_LEVEL env var controls verbosity

📁 Expected files to change/structure

• backend/src/health/health.module.ts
• backend/src/health/health.controller.ts
• backend/src/main.ts
• backend/.env.example (add LOG_LEVEL)

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Commit: chore: add health check endpoint and structured logging to backend
Branch: chore/backend-health-and-logging | Priority: LOW | Difficulty: one-coffee

[Listoncrypt]

@Listoncrypt has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello, I would love to take on this issue and expect a PR within a few hours.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Listoncrypt to this issue.

[drips-wave]

Congratulations, @Listoncrypt! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

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