Add health check endpoint and structured logging

[trsdn]

Summary

Improve observability with health checks and structured JSON logging.

Tasks

• Add GET /api/health endpoint with status, uptime, and version
• Add GET /api/ready readiness check (Copilot client connected)
• Replace console.log with structured logger (pino or winston)
• Add request ID tracking for tracing
• Add log levels (debug, info, warn, error)
• Add environment-based log configuration

Acceptance Criteria

• /api/health returns { status: "healthy", uptime: X, version: "1.0.0" }
• /api/ready returns 200 when Copilot client is connected, 503 otherwise
• All logs are JSON formatted with timestamps and request IDs
• Log level configurable via LOG_LEVEL env var