PARKED: Event metrics overlay chart (recon Part A)

Parked on 2026-06-12 per Richie. Add an event-report overlay chart reusing SiteEnergyCharts primitives, scoped to event-participant devices/sites. Recon confirmed four energy resolvers already accept deviceId[]/siteId[] filters — no schema work needed. Path: project siteProfileId in deviceResolver.getDevicesFromBatches, then build chart. Effort ~1-2 days. Recon doc: recon/2026-06-12-event-metrics-kpi.md (Part A). NO Linear ticket yet — file when Richie greenlights.