Fix scrolling and keep lists clear of the scrollbar

Scroll kept its position as an int, so wheel and trackpad deltas were
truncated: small ones were lost in one direction and a wheel notch moved
one unit. It now keeps a fractional position, scrolls 24 units a notch,
sizes and places its thumb consistently, and the thumb can be dragged or
the track clicked. PanelScreen's scrollWidth and scrollContentWidth keep
every scrolling list clear of the bar.

Sliders read a float step from its text, so 0.1 no longer shows 17
decimals, and show at most three; number boxes show at most three too.

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

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

@@ -3,6 +3,7 @@ package org.saturnclient.ui;
 import org.saturnclient.ui.components.Sidebar;
 import org.saturnclient.ui.elements.ImageTexture;
 import org.saturnclient.ui.elements.Panel;
+import org.saturnclient.ui.elements.Scroll;
 import org.saturnclient.ui.resources.Textures;
 
 /**
@@ -18,6 +19,9 @@ public abstract class PanelScreen extends SaturnScreen {
 
     protected static final int PADDING = 20;
 
+    /** How far a scroll reaches past its content area, into the padding, for its bar */
+    private static final int SCROLL_OVERHANG = 14;
+
     private final int sidebarItem;
 
     protected int panelX, panelY, panelWidth, panelHeight;
@@ -61,4 +65,18 @@ public abstract class PanelScreen extends SaturnScreen {
      * Draws the panel's content.
      */
     protected abstract void panel();
+
+    /**
+     * The width of a scroll filling {@code width} of the content area.
+     */
+    protected static int scrollWidth(int width) {
+        return width + SCROLL_OVERHANG;
+    }
+
+    /**
+     * The width left for a scroll's children, clear of its scrollbar.
+     */
+    protected static int scrollContentWidth(int width) {
+        return scrollWidth(width) - Scroll.SCROLLBAR_SPACE;
+    }
 }