Stop a row of buttons deciding how wide the grid is

**A Slint layout cannot be narrower than its children's minimums.** Given
less room than they need it lays them out at those minimums, lets the row
run past the edge — and reports the oversized minimum upwards.

That second half is what made this more than cosmetic. The header, the
filter chips and the grid are siblings in one VerticalLayout, so the
widest row's minimum became the whole view's minimum: `LibraryGrid` was
laid out wider than the window. The grid then measured itself against
that inflated box and sized its columns to fill space that was off the
screen, so the right-hand column was cut by the edge no matter what the
tiling arithmetic did. Fourteen filter chips do not fit across 768
logical pixels, so that was every tablet in portrait.

It also explains why opening the collections sidebar did not reflow the
grid. The view was already pinned at a minimum wider than the window, so
taking 232px away for the sidebar could not shrink it — it just clipped
more of it.

Each of those rows is now a horizontal Flickable. A Flickable's own
minimum is nothing, since it exists to be smaller than what it holds, so
none of them can inflate anything — and the controls past the edge became
reachable instead of merely absent. Applied to all four: the library
header, the filter chips, the compact action row disclosed by "More", and
the develop strip.

ui/dr-ui/ui/app.slint

@@ -64,7 +64,21 @@ component StatusBar inherits Rectangle {
     height: 44px;
     background: Theme.surface;
 
-    HorizontalLayout {
+    // Scrolls rather than overflowing. A layout given less width than its
+    // children need does not shrink them — it overruns the edge and reports
+    // the oversized minimum to whatever contains it. Collapsing the
+    // instrumentation below buys back about 200 logical pixels, which is
+    // enough for a tablet; it is not enough for a phone, and nothing here
+    // should be unreachable merely because the window is narrow.
+    Flickable {
+        width: 100%;
+        height: 100%;
+        viewport-height: self.height;
+        viewport-width: max(self.width, strip.preferred-width);
+
+    strip := HorizontalLayout {
+        width: parent.viewport-width;
+        height: parent.viewport-height;
         padding-left: Theme.gap;
         padding-right: Theme.gap;
         spacing: Theme.gap;
@@ -204,6 +218,7 @@ component StatusBar inherits Rectangle {
         }
 
     }
+    }
 
     Rectangle {
         y: parent.height - 1px;