Issue #54 — Health check endpoint

[GoSTEAN]

Title: [Middleware] Implement health check and readiness probe endpoints

Tags: backend, feature, good first issue

Description:
Kubernetes-compatible health and readiness endpoints for load balancers and orchestration.

Acceptance Criteria:

• GET /health — liveness probe; returns 200 { status: "ok", uptime } always (even during DB issues).
• GET /health/ready — readiness probe; checks DB, Redis, and Stellar RPC; returns 200 if all pass, 503 if any fail.
• No auth required on either endpoint.
• Response includes: { status, db, redis, stellar, version }.

File: src/routes/health.routes.ts

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