feat: implement waterfall layout with smart image positioning and infinite scroll

- Add single-column layout for homepage articles
- Implement smart image positioning based on aspect ratio:
  * Landscape images (ratio > 1.2) displayed on top
  * Portrait/square images (ratio ≤ 1.2) displayed on left side
- Add infinite scroll with lazy loading
- Create new API endpoint /api/articles for pagination
- Add loading indicator and 'no more articles' message
- Optimize performance with image lazy loading and scroll throttling
- Add responsive layout for mobile devices

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

main.go

@@ -50,6 +50,9 @@ func main() {
 
 	// 8. Register routes.
 	router.GET("/", handlers.HomePage(db))
+	router.GET("/api/articles", handlers.HomeArticlesAPI(db))
+	router.GET("/rss", handlers.RSSFeed(db))
+	router.GET("/feed", handlers.RSSFeed(db))
 	router.GET("/login", handlers.LoginPage())
 	router.POST("/login", handlers.Login(db))
 	router.POST("/logout", handlers.Logout())