feat: GeoScene frontend POC + Docker deploy for remote host

Migrate maps to @geoscene/core, polish monitoring/alerts UX, fix timeline
basemap flicker and district alert regions, and ship compose/nginx Docker
deploy assets with CBPOA_ROOT data mounts.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/package.json

@@ -9,12 +9,11 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@geoscene/core": "4.32.10",
     "axios": "^1.6.7",
-    "leaflet": "^1.9.4",
     "lucide-react": "^0.330.0",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
-    "react-leaflet": "^4.2.1",
     "react-router-dom": "^6.30.4",
     "recharts": "^2.12.0",
     "zustand": "^4.5.0"
@@ -23,7 +22,6 @@
     "@playwright/test": "^1.59.1",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^14.3.1",
-    "@types/leaflet": "^1.9.8",
     "@types/react": "^18.2.55",
     "@types/react-dom": "^18.2.19",
     "@vitejs/plugin-react": "^4.2.1",