Add publish_date and expiry_date support

app/content.php

@@ -120,7 +120,10 @@ function buildNavigation(Context $ctx): array {
         
         $itemPath = "{$ctx->contentDir}/$item";
         $metadata = loadMetadata($itemPath);
-        
+
+        // Skip invisible content (future publish or expired)
+        if (!isVisible($metadata)) continue;
+
         // Only include if explicitly marked as menu item
         // parse_ini_file returns boolean true as 1, false as empty string, and "true"/"false" as strings
         if (!$metadata || !isset($metadata['menu']) || !$metadata['menu']) {