feat: resolve NIP-19 identifiers in article content

- Add nostrUriResolver utility to detect and replace nostr: URIs
- Support npub, note, nprofile, nevent, and naddr identifiers
- Convert nostr: URIs to clickable njump.me links
- Process markdown before rendering to handle nostr mentions
- Add CSS styling for nostr-uri-link class
- Implements NIP-19 and NIP-27 (nostr: URI scheme)

Nostr-native articles can now contain references like:
- nostr:npub1... → @npub1abc...
- nostr:note1... → note:note1abc...
- nostr:naddr1... → article:identifier

All identifiers become clickable links to njump.me

src/components/ContentPanel.tsx

@@ -59,7 +59,7 @@ const ContentPanel: React.FC<ContentPanelProps> = ({
   onTextSelection,
   onClearSelection
 }) => {
-  const { renderedHtml: renderedMarkdownHtml, previewRef: markdownPreviewRef } = useMarkdownToHTML(markdown)
+  const { renderedHtml: renderedMarkdownHtml, previewRef: markdownPreviewRef, processedMarkdown } = useMarkdownToHTML(markdown)
   
   const { finalHtml, relevantHighlights } = useHighlightedContent({
     html,
@@ -116,7 +116,7 @@ const ContentPanel: React.FC<ContentPanelProps> = ({
       {markdown && (
         <div ref={markdownPreviewRef} style={{ display: 'none' }}>
           <ReactMarkdown remarkPlugins={[remarkGfm]}>
-            {markdown}
+            {processedMarkdown || markdown}
           </ReactMarkdown>
         </div>
       )}