feat: add route selection functionality and improve station handling

- Added `vitest` for testing and created initial tests for route utilities.
- Implemented route selection logic in the App component, allowing users to select start and end stations.
- Updated the NetworkMap component to reflect focused and selected stations, including visual indicators for start and end stations.
- Enhanced the route panel UI to display selected route information and estimated lengths.
- Introduced utility functions for building track adjacency and computing routes based on selected stations.
- Improved styling for route selection and station list items to enhance user experience.

frontend/package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview",
     "lint": "eslint \"src/**/*.{ts,tsx}\"",
     "format": "prettier --write \"src/**/*.{ts,tsx,css}\"",
+    "test": "vitest run",
     "test:e2e": "playwright test"
   },
   "dependencies": {
@@ -34,6 +35,7 @@
     "eslint-plugin-react-hooks": "^4.6.2",
     "prettier": "^3.3.3",
     "typescript": "^5.5.3",
-    "vite": "^5.4.0"
+    "vite": "^5.4.0",
+    "vitest": "^1.6.0"
   }
 }