Capacity planning dashboard spec

RU utilization: Per site, sum of assigned positions vs total RU (from racks); show percentage. Implemented. API: GET /api/v1/capacity/sites/:siteId returns usedRu, totalRu, and utilizationPercent.
Power headroom: From rack power_feeds (circuit limits). Implemented. API: GET /api/v1/capacity/sites/:siteId/power returns circuitLimitWatts, measuredDrawWatts (null until Phase 4), headroomWatts (null). Measured draw can be added when telemetry is available.
GPU inventory: By type (part number) and location. Implemented. API: GET /api/v1/capacity/gpu-inventory returns total, bySite, and byType.
Read-only: All capacity endpoints are read-only; no edits.
Web: Capacity dashboard at /capacity shows RU utilization, power headroom, and GPU inventory by site and type.