Add dropdowns and a popup color picker

Popup draws one element above the rest of the screen and gets mouse
events first; clicking or scrolling outside closes it. ElementContext now
carries each element's position on screen so an input inside a scroll can
open a popup beside itself.

Select is a dropdown: the current value opens an OptionList with the
current option ticked, scrolling for long lists and opening upward when
there's no room below. The color picker moved out of ColorInput into a
ColorPicker popup, so scroll areas no longer clip it and later rows no
longer draw over it, and all three of its parts can be dragged.

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

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

@@ -15,6 +15,15 @@ public class ElementRenderer {
     }
 
     public static void render(List<Element> elements, long elapsed, RenderScope renderScope, int mouseX, int mouseY) {
+        render(elements, elapsed, renderScope, mouseX, mouseY, 0, 0);
+    }
+
+    /**
+     * Renders elements whose parent's top-left corner is at
+     * ({@code parentX}, {@code parentY}) on the screen.
+     */
+    public static void render(List<Element> elements, long elapsed, RenderScope renderScope, int mouseX, int mouseY,
+            int parentX, int parentY) {
         for (Element element : elements) {
             element.playAnimationFrame(elapsed);
 
@@ -22,7 +31,7 @@ public class ElementRenderer {
             renderScope.setOpacity(element.opacity);
             renderScope.getMatrixStack().translate(element.x, element.y);
             renderScope.getMatrixStack().scale(element.scale, element.scale);
-            element.render(renderScope, new ElementContext(elapsed, mouseX, mouseY, element));
+            element.render(renderScope, new ElementContext(elapsed, mouseX, mouseY, parentX, parentY, element));
             renderScope.getMatrixStack().pop();
         }
     }