fix: show highlights for nostr articles by skipping URL filter

The HighlightsPanel was filtering out ALL highlights that didn't have
a urlReference. But Nostr article highlights reference the article via
the 'a' tag (article coordinate), not a URL.

Since we already fetch highlights specifically for the current article
using fetchHighlightsForArticle(), we don't need to filter them again.

Solution:
- Skip URL filtering when selectedUrl starts with 'nostr:'
- Keep URL filtering for web articles (backwards compatible)
- Highlights are already pre-filtered by the fetch query

This fixes the issue where 101 highlights existed for the default
article but weren't being displayed in the UI.

src/components/HighlightsPanel.tsx

@@ -37,10 +37,17 @@ export const HighlightsPanel: React.FC<HighlightsPanelProps> = ({
     onToggleUnderlines?.(newValue)
   }
   
-  // Filter highlights to show only those relevant to the current URL
+  // Filter highlights to show only those relevant to the current URL or article
   const filteredHighlights = useMemo(() => {
     if (!selectedUrl) return highlights
     
+    // For Nostr articles (URL starts with "nostr:"), we don't need to filter
+    // because we already fetched highlights specifically for this article
+    if (selectedUrl.startsWith('nostr:')) {
+      return highlights
+    }
+    
+    // For web URLs, filter by URL matching
     const normalizeUrl = (url: string) => {
       try {
         const urlObj = new URL(url.startsWith('http') ? url : `https://${url}`)