feat(health): implement GET /live and /ready health probes (#334)

[sparkysolutions10-pixel]

Closes #334

Summary of Changes

• Implements /live probe answering 200 { "status": "live" } without database or external dependency overhead.
• Implements /ready probe checking boot initialization lifecycle (src/bootState.ts) and active connectivity to PostgreSQL and Redis.
  • Returns 503 { "status": "unhealthy", "checks": { "database": ..., "redis": ... } } during boot or when Postgres is down.
  • Returns 200 { "status": "ready", ... } once boot completes and dependencies are reachable.
• Both /live and /ready are marked public: true, allowlisted from the rate limiter in src/app.ts, and excluded from httpMetrics route cardinality in src/middleware/httpMetrics.ts.
• Preserves /status unchanged.
• Fully registered in openapi.yaml/openapi.json and verified with automated unit tests in src/__tests__/healthProbes.test.ts.