feat: configure default article via environment variable

- Add VITE_DEFAULT_ARTICLE_NADDR env variable support
- Create .env with default article naddr
- Create .env.example for documentation
- Add vite-env.d.ts for TypeScript type support
- Fallback to hardcoded value if env var not set
- Using Vite's built-in env variable support (no dotenv needed)

.env.example

@@ -0,0 +1,3 @@
+# Default article to display on app load
+# This should be a valid naddr1... string (NIP-19 encoded address pointer to a kind:30023 long-form article)
+VITE_DEFAULT_ARTICLE_NADDR=naddr1qvzqqqr4gupzqmjxss3dld622uu8q25gywum9qtg4w4cv4064jmg20xsac2aam5nqqxnzd3cxqmrzv3exgmr2wfesgsmew

src/App.tsx

@@ -8,7 +8,9 @@ import { createAddressLoader } from 'applesauce-loaders/loaders'
 import Login from './components/Login'
 import Bookmarks from './components/Bookmarks'
 
-const DEFAULT_ARTICLE = 'naddr1qvzqqqr4gupzqmjxss3dld622uu8q25gywum9qtg4w4cv4064jmg20xsac2aam5nqqxnzd3cxqmrzv3exgmr2wfesgsmew'
+// Load default article from environment variable with fallback
+const DEFAULT_ARTICLE = import.meta.env.VITE_DEFAULT_ARTICLE_NADDR || 
+  'naddr1qvzqqqr4gupzqmjxss3dld622uu8q25gywum9qtg4w4cv4064jmg20xsac2aam5nqqxnzd3cxqmrzv3exgmr2wfesgsmew'
 
 function App() {
   const [eventStore, setEventStore] = useState<EventStore | null>(null)

src/vite-env.d.ts

@@ -0,0 +1,9 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_DEFAULT_ARTICLE_NADDR: string
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv
+}