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>

backend/scripts/convert_power_plants.py

@@ -0,0 +1,58 @@
+"""Download WRI Global Power Plant Database CSV and convert to compact JSON.
+
+Usage:
+    python backend/scripts/convert_power_plants.py
+
+Output:
+    backend/data/power_plants.json
+"""
+import csv
+import json
+import io
+import zipfile
+import urllib.request
+from pathlib import Path
+
+# WRI Global Power Plant Database v1.3.0 (GitHub release)
+CSV_URL = "https://raw.githubusercontent.com/wri/global-power-plant-database/master/output_database/global_power_plant_database.csv"
+OUT_PATH = Path(__file__).parent.parent / "data" / "power_plants.json"
+
+
+def main() -> None:
+    print(f"Downloading WRI Global Power Plant Database from GitHub...")
+    req = urllib.request.Request(CSV_URL, headers={"User-Agent": "ShadowBroker-OSINT/1.0"})
+    with urllib.request.urlopen(req, timeout=60) as resp:
+        raw = resp.read().decode("utf-8")
+
+    reader = csv.DictReader(io.StringIO(raw))
+    plants: list[dict] = []
+    skipped = 0
+    for row in reader:
+        try:
+            lat = float(row["latitude"])
+            lng = float(row["longitude"])
+        except (ValueError, KeyError):
+            skipped += 1
+            continue
+        if not (-90 <= lat <= 90 and -180 <= lng <= 180):
+            skipped += 1
+            continue
+        capacity_raw = row.get("capacity_mw", "")
+        capacity_mw = float(capacity_raw) if capacity_raw else None
+        plants.append({
+            "name": row.get("name", "Unknown"),
+            "country": row.get("country_long", ""),
+            "fuel_type": row.get("primary_fuel", "Unknown"),
+            "capacity_mw": capacity_mw,
+            "owner": row.get("owner", ""),
+            "lat": round(lat, 5),
+            "lng": round(lng, 5),
+        })
+
+    OUT_PATH.parent.mkdir(parents=True, exist_ok=True)
+    OUT_PATH.write_text(json.dumps(plants, ensure_ascii=False, separators=(",", ":")), encoding="utf-8")
+    print(f"Wrote {len(plants)} power plants to {OUT_PATH} (skipped {skipped})")
+
+
+if __name__ == "__main__":
+    main()