Add long-form article editor (NIP-23)

- ArticleEditor with title, markdown body, summary, cover image, tags
- write/preview toggle with markdown rendering via marked
- Auto-save draft to localStorage
- Publish as kind 30023 with NIP-23 tags (d, title, published_at, etc.)
- 'write article' button in sidebar when logged in
- Article preview prose styles in CSS

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

package.json

@@ -14,6 +14,7 @@
     "@tailwindcss/vite": "^4.2.1",
     "@tauri-apps/api": "^2",
     "@tauri-apps/plugin-opener": "^2",
+    "marked": "^17.0.4",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",
     "tailwindcss": "^4.2.1",
@@ -21,6 +22,7 @@
   },
   "devDependencies": {
     "@tauri-apps/cli": "^2",
+    "@types/marked": "^5.0.2",
     "@types/react": "^19.1.8",
     "@types/react-dom": "^19.1.6",
     "@vitejs/plugin-react": "^4.6.0",