test: keep Vite env helper in frontend project

app/game-frontend/src/config/viteEnv.ts

@@ -0,0 +1,7 @@
+export const mergeViteEnv = (
+    fileEnv: Record<string, string>,
+    runtimeEnv: NodeJS.ProcessEnv
+): Record<string, string | undefined> => ({
+    ...fileEnv,
+    ...runtimeEnv,
+});