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/hooks/useMarkdownToHTML.ts

@@ -1,18 +1,30 @@
 import React, { useState, useEffect, useRef } from 'react'
+import { replaceNostrUrisInMarkdown } from '../utils/nostrUriResolver'
 
 /**
  * Hook to convert markdown to HTML using a hidden ReactMarkdown component
+ * Also processes nostr: URIs in the markdown
  */
-export const useMarkdownToHTML = (markdown?: string): { renderedHtml: string, previewRef: React.RefObject<HTMLDivElement> } => {
+export const useMarkdownToHTML = (markdown?: string): { 
+  renderedHtml: string
+  previewRef: React.RefObject<HTMLDivElement>
+  processedMarkdown: string 
+} => {
   const previewRef = useRef<HTMLDivElement>(null)
   const [renderedHtml, setRenderedHtml] = useState<string>('')
+  const [processedMarkdown, setProcessedMarkdown] = useState<string>('')
 
   useEffect(() => {
     if (!markdown) {
       setRenderedHtml('')
+      setProcessedMarkdown('')
       return
     }
 
+    // Process nostr: URIs in markdown before rendering
+    const processed = replaceNostrUrisInMarkdown(markdown)
+    setProcessedMarkdown(processed)
+
     console.log('📝 Converting markdown to HTML...')
     
     const rafId = requestAnimationFrame(() => {
@@ -28,7 +40,7 @@ export const useMarkdownToHTML = (markdown?: string): { renderedHtml: string, pr
     return () => cancelAnimationFrame(rafId)
   }, [markdown])
 
-  return { renderedHtml, previewRef }
+  return { renderedHtml, previewRef, processedMarkdown }
 }
 
 // Removed separate useMarkdownPreviewRef; use useMarkdownToHTML to obtain previewRef