Add complete health check implementation for Docker HEALTHCHECK and
Traefik health routing with:
Response fields:
- status: "ok" or "degraded"
- uptime_s: seconds since mothership boot
- version: mothership version string
- nodes_online: count of connected nodes
- db: "ok" or "failing" (SELECT 1 with 100ms timeout)
- load_level: 0-3 from load shedding state
- reason: human-readable explanation (only when degraded)
HTTP status codes:
- 200 for healthy (status="ok")
- 503 for degraded (status="degraded")
Degraded conditions:
- Database unreachable
- Load level 3 sustained for >60 seconds
- No nodes connected after 5 minutes uptime
Docker HEALTHCHECK updated to verify status="ok" response.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
