Add long-form article reader (Phase 1 #1, NIP-23)

- fetchArticle(naddr): fetches kind 30023 by d-tag + author pubkey
- fetchAuthorArticles(pubkey): for future profile articles tab
- ArticleView: cover image, title, italic summary, author row (avatar +
  name + date), tag pills, full markdown body (DOMPurify sanitized),
  zap author button in header and footer, copy nostr: link, njump.me
  fallback on fetch error
- prose-article CSS: reader-optimised typography (15px base, 1.8 line
  height, h2 border, styled blockquote/code/pre/links/images)
- NoteContent: naddr1 clicks for kind 30023 now open ArticleView
  instead of falling through to njump.me
- openArticle(naddr) added to UI store with previousView tracking

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -14,6 +14,8 @@
     "@tailwindcss/vite": "^4.2.1",
     "@tauri-apps/api": "^2",
     "@tauri-apps/plugin-opener": "^2",
+    "@types/dompurify": "^3.0.5",
+    "dompurify": "^3.3.2",
     "marked": "^17.0.4",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",