Give the strip a layout to sit in

The develop column's panel is a Rectangle, not a layout — a note four lines
above explains why it is not an `if`. Two children of one therefore both sit
at its origin, so pinning the strip beside the Flickable overlapped them and
collapsed the whole develop view to a sliver.

Wrapped in a VerticalLayout. The strip is pinned by being outside the
Flickable rather than by any coordinate, which is what keeps it working at
any column height.

Caught by screenshotting the device rather than by the build, which was
clean throughout — a Slint layout fault is invisible in the source and
obvious the moment anyone looks.

ui/dr-ui/ui/app.slint

@@ -1839,6 +1839,10 @@ in property <bool> panel-visible: true;
                     // the column instead.
                     // Pinned: the strip is how the column is navigated, so it
                     // cannot be somewhere you have to navigate to.
+                    // A layout, because the parent is a Rectangle: two children of one
+                    // would both sit at its origin and overlap. The strip is pinned by
+                    // being outside the Flickable rather than by any coordinate.
+                    VerticalLayout {
                         GroupStrip {
                             enabled: root.adjust-enabled;
                             tabs: root.adjust-tabs;
@@ -1991,6 +1995,7 @@ in property <bool> panel-visible: true;
                             }
                             }
                         }
+                    }
 
                     Rectangle {
                         width: 1px;