fix: remove react-leaflet-cluster dependency conflict

- Remove react-leaflet-cluster package incompatible with React 19
- Update MapView component to use standard react-leaflet markers
- Remove react-leaflet-cluster mock from tests
- Frontend now builds successfully without dependency conflicts

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

frontend/package.json

@@ -13,7 +13,6 @@
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-leaflet": "^5.0.0",
-    "react-leaflet-cluster": "^1.0.3",
     "react-router-dom": "^6.28.0",
     "react-scripts": "5.0.1",
     "react-toastify": "^11.0.5",