Implement Advanced Healthchecks with Dependency Checks

[carlos-israelj]

Description

Basic healthcheck exists but doesn't check dependencies (database, Redis, Horizon). Service reports healthy even when critical dependencies are down.

Current State

Simple /health endpoint.

Problems

• No dependency health checks
• False positives (app healthy but DB down)
• No detailed status
• No alerting

Proposed Solution

Advanced healthcheck endpoint that validates all dependencies.

Acceptance Criteria

• /health/live (liveness check)
• /health/ready (readiness check with dependencies)
• Check PostgreSQL connection
• Check Redis connection
• Check Horizon API reachability
• JSON response with detailed status
• Integration with monitoring (Uptime Kuma, etc.)

ETA

3-5 days