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>

src/App.tsx

@@ -4,6 +4,7 @@ import { RelaysView } from "./components/shared/RelaysView";
 import { SettingsView } from "./components/shared/SettingsView";
 import { ProfileView } from "./components/profile/ProfileView";
 import { ThreadView } from "./components/thread/ThreadView";
+import { ArticleEditor } from "./components/article/ArticleEditor";
 import { useUIStore } from "./stores/ui";
 
 function App() {
@@ -18,6 +19,7 @@ function App() {
         {currentView === "settings" && <SettingsView />}
         {currentView === "profile" && <ProfileView />}
         {currentView === "thread" && <ThreadView />}
+        {currentView === "article-editor" && <ArticleEditor />}
       </main>
     </div>
   );