feat: enhance MapViewer with city selection and layout integration

- Added support for city selection in MapViewer, allowing users to click on cities to view details.
- Integrated map layout data to improve city rendering and positioning.
- Introduced SelectedCityPanel to display information about the selected city.
- Updated map asset handling with utility functions for building asset URLs.
- Enhanced state management in mapViewer store to track selected city.
- Improved responsiveness and styling of map components.
- Added new API endpoint for loading map layouts from legacy data.

app/game-frontend/src/utils/mapAssets.ts

@@ -0,0 +1,21 @@
+const normalizeBase = (value: string | undefined | null): string => {
+    const base = (value ?? '').trim();
+    return base.replace(/\/+$/, '');
+};
+
+export const buildAssetUrl = (base: string | undefined | null, path: string): string => {
+    const normalizedBase = normalizeBase(base);
+    const normalizedPath = path.replace(/^\/+/, '');
+    if (!normalizedBase) {
+        return `/${normalizedPath}`;
+    }
+    return `${normalizedBase}/${normalizedPath}`;
+};
+
+export const normalizeColorToken = (color: string | undefined | null): string | null => {
+    if (!color) {
+        return null;
+    }
+    const cleaned = color.trim().replace(/^#/, '').toUpperCase();
+    return cleaned.length > 0 ? cleaned : null;
+};