Health check endpoint for monitoring and load balancers.

Returns:

• uptime: Server uptime in seconds and human-readable format
• renewal: Background renewal service status
• tradingview: TradingView CLI connectivity status
• database: SQLite connectivity (always "connected" once running)
• last_data_refresh: Timestamps of last data fetch per symbol

Usage: curl http://localhost:8001/health curl -s http://localhost:8001/health | python -m json.tool

For Kubernetes/liveness probes: curl -f http://localhost:8001/health

For detailed checks: curl -s http://localhost:8001/health | jq '.renewal'