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/index.css

@@ -479,6 +479,23 @@ body.mobile-sidebar-open {
   text-decoration: underline;
 }
 
+.nostr-uri-link {
+  color: #007bff;
+  text-decoration: none;
+  font-family: monospace;
+  background: #f8f9fa;
+  padding: 0.2rem 0.4rem;
+  border-radius: 4px;
+  font-size: 0.9em;
+  word-wrap: break-word;
+  overflow-wrap: break-word;
+}
+
+.nostr-uri-link:hover {
+  background: #e9ecef;
+  text-decoration: underline;
+}
+
 .logout-button {
   background: #dc3545;
   color: white;