Ruff auto-fix: unused Optional imports in sectors router and link
schemas, unused Site import in device service, unused datetime
imports in trend detector, unused text import in site service,
and f-string without placeholders in signal history service.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Add site_service with CRUD, health rollup, device assignment functions
- Add sites router with 8 endpoints (CRUD + assign/unassign/bulk-assign)
- RBAC: viewer for reads, operator for writes, tenant_admin for delete
- Wire sites_router into main.py with /api prefix
- Health rollup computes device_count, online_count, online_percent per site
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
