feat: add power plants layer with WRI Global Power Plant Database

Map ~35,000 power generation facilities from 164 countries using the
WRI Global Power Plant Database (CC BY 4.0). Follows the existing
datacenter layer pattern with clustered icon symbols, amber color
scheme, and click popups showing fuel type, capacity, and operator.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/map/geoJSONBuilders.ts

@@ -2,7 +2,7 @@
 // Extracted from MaplibreViewer to reduce component size and enable unit testing.
 // Each function takes data arrays + optional helpers and returns a GeoJSON FeatureCollection or null.
 
-import type { Earthquake, GPSJammingZone, FireHotspot, InternetOutage, DataCenter, MilitaryBase, GDELTIncident, LiveUAmapIncident, CCTVCamera, KiwiSDR, FrontlineGeoJSON, UAV, Satellite, Ship, ActiveLayers } from "@/types/dashboard";
+import type { Earthquake, GPSJammingZone, FireHotspot, InternetOutage, DataCenter, MilitaryBase, PowerPlant, GDELTIncident, LiveUAmapIncident, CCTVCamera, KiwiSDR, FrontlineGeoJSON, UAV, Satellite, Ship, ActiveLayers } from "@/types/dashboard";
 import { classifyAircraft } from "@/utils/aircraftClassification";
 import { MISSION_COLORS, MISSION_ICON_MAP } from "@/components/map/icons/SatelliteIcons";
 
@@ -195,6 +195,28 @@ export function buildDataCentersGeoJSON(datacenters?: DataCenter[]): FC {
     };
 }
 
+// ─── Power Plants ──────────────────────────────────────────────────────────
+
+export function buildPowerPlantsGeoJSON(plants?: PowerPlant[]): FC {
+    if (!plants?.length) return null;
+    return {
+        type: 'FeatureCollection',
+        features: plants.map((p, i) => ({
+            type: 'Feature' as const,
+            properties: {
+                id: `pp-${i}`,
+                type: 'power_plant',
+                name: p.name || 'Unknown',
+                country: p.country || '',
+                fuel_type: p.fuel_type || 'Unknown',
+                capacity_mw: p.capacity_mw ?? 0,
+                owner: p.owner || '',
+            },
+            geometry: { type: 'Point' as const, coordinates: [p.lng, p.lat] }
+        }))
+    };
+}
+
 // ─── Military Bases ─────────────────────────────────────────────────────────
 
 // Classify base alignment: red = adversary, blue = US/allied, green = ROC