feat: throw explicit error when SITE_DOMAIN is unset

- Throw fatal configuration error in src/_data/site.js if SITE_DOMAIN is missing
- Require SITE_DOMAIN in docker-compose.yml without default fallback
- Require SITE_DOMAIN ARG in Dockerfile with no default fallback

src/_data/site.js

@@ -21,7 +21,17 @@ try {
   // Silent fallback
 }
 
-const siteDomain = process.env.SITE_DOMAIN || "riverrooks.dev";
+const siteDomain = process.env.SITE_DOMAIN;
+if (!siteDomain) {
+  throw new Error(
+    "\n=======================================================================\n" +
+    "FATAL CONFIGURATION ERROR: SITE_DOMAIN environment variable is not set.\n" +
+    "The site domain must be explicitly defined in your .env file or environment.\n" +
+    "Example in .env:\n" +
+    "  SITE_DOMAIN=riverrooks.dev\n" +
+    "=======================================================================\n"
+  );
+}
 const siteUrl = process.env.SITE_URL || `https://${siteDomain}`;
 
 export default {