Leave the adjust panel somewhere to scroll from

A strip down the right-hand edge of the panel that no control reaches, so
there is always somewhere to put a thumb that means "scroll" and nothing
else.

This is the other half of the slider arbitration. A `SliderTrack` stands
the Flickable down the moment a finger touches it, which is what makes
dragging an adjustment reliable — and the price is that the track can no
longer be dragged past. What was left to scroll from was the ~20px band of
label between one control and the next, which on a panel that is mostly
tracks means aiming rather than reaching. Reserving the space outright is
the honest version of what had been left to chance.

Padding rather than a spacer element, and that is what makes it work: the
strip is inside the Flickable but no child is laid out into it, so nothing
puts a TouchArea over it. A press there reaches the Flickable directly,
with no arbitration to lose.

A full touch target wide (FR-UI-3). A gutter too narrow to hit confidently
would be the problem it was added to fix, in a smaller space. It costs the
tracks about 44px of a 280px column, which leaves travel enough that the
readout still moves a step per pixel at the precisions the descriptors ask
for.

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

ui/dr-ui/ui/adjust.slint

@@ -728,6 +728,31 @@ export component AdjustPanel inherits Rectangle {
                 spacing: 0px;
                 alignment: start;
 
+                // **The scroll gutter.**
+                //
+                // A strip down the right-hand edge that no control reaches, so
+                // there is always somewhere to put a thumb that means "scroll"
+                // and nothing else.
+                //
+                // It exists because of the arbitration in `SliderTrack`: a
+                // track stands the Flickable down as soon as a finger touches
+                // it, which is what makes dragging a slider reliable, and the
+                // cost is that the track can no longer be used to scroll past.
+                // The rows either side of a track were the only remaining
+                // purchase, and on a panel that is mostly tracks that came to
+                // aiming at a 20px band between controls. Reserving the space
+                // outright is the honest version of what was left to chance.
+                //
+                // Padding rather than a spacer element, and that is what makes
+                // it work: the strip is inside the Flickable but no child is
+                // laid out into it, so nothing puts a TouchArea over it. A
+                // press there reaches the Flickable directly, with no
+                // arbitration to lose.
+                //
+                // A full touch target wide (FR-UI-3), because a gutter too
+                // narrow to hit confidently is the problem it was added to fix.
+                padding-right: Theme.touch-target;
+
                 // One iteration per row, but only a group's *first* row draws
                 // anything — and it draws the whole group. Every other row
                 // renders nothing at all.