PIV Image Sync Worker v3

Endpoints:
  GET  /health              Health check
  GET  /status              Sync progress
  POST /sync                Start/resume sync
  POST /sync?reset=true     Reset and restart
  POST /sync?trust=true     Skip HEAD checks (faster)
  POST /cleanup             Remove orphans
  POST /cleanup?dry=true    Preview orphan cleanup
  GET  /villas/*            Serve images

All POST endpoints require X-API-Key header.