web/vite.config: enforce WEB_DEFAULT_URL variable

web/vite.config.ts

@@ -77,8 +77,20 @@ const generateSitemap: PluginOption = {
     }
 }
 
+const checkDefaultApiEnv = (): PluginOption => ({
+    name: "check-default-api",
+    config() {
+        if (!process.env.WEB_DEFAULT_API) {
+            throw new Error(
+                "WEB_DEFAULT_API env variable is required, but missing."
+            );
+        }
+    },
+});
+
 export default defineConfig({
     plugins: [
+        checkDefaultApiEnv(),
         basicSSL(),
         sveltekit(),
         enableCOEP,