Remove UI code and icons nothing uses

TextureButton, ClickableTexture, Text, Notification and the FadeOut and
SlideX animations only Notification used, Utils.getOrNull and the
commented-out notify, Element.duration, the 17 PNG icons the Lucide SVGs
replaced, and the Textures constants for them and for files that don't
exist.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/main/java/org/saturnclient/ui/Element.java

@@ -11,7 +11,6 @@ public class Element {
     public boolean focused;
     public Animation animation;
     public float scale = 1.0f;
-    public Integer duration = null; // Element duration, will fade out if not null
 
     public void render(RenderScope renderScope, ElementContext ctx) {
     }