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/ElementContext.java

@@ -2,13 +2,17 @@ package org.saturnclient.ui;
 
 public class ElementContext {
     public int mouseX, mouseY;
+    /** The element's top-left corner on the screen, for placing popups next to it */
+    public int originX, originY;
     public int elementWidth, elementHeight;
     public float elementScale;
     public long elapsed;
 
-    public ElementContext(long elapsed, int mouseX, int mouseY, Element e) {
+    public ElementContext(long elapsed, int mouseX, int mouseY, int parentX, int parentY, Element e) {
         this.mouseX = mouseX - e.x;
         this.mouseY = mouseY - e.y;
+        this.originX = parentX + e.x;
+        this.originY = parentY + e.y;
         this.elementWidth = e.width;
         this.elementHeight = e.height;
         this.elementScale = e.scale;