Put a scrollbar on the settings page

The page is several screens long, and nothing said so until something
had been scrolled. Same wrapping as the develop column; the bar sits at
the window's right edge, clear of the capped 680px form.

docs/gestures.md

@@ -786,4 +786,4 @@ The badge on a cell says a photograph is filed in three collections and never wh
 
 Beside the other whole-library passes, because it is one; the sidebar offers the same page under the trash.
 
-<sub>`ui/dr-ui/ui/settings.slint:530`</sub>
+<sub>`ui/dr-ui/ui/settings.slint:533`</sub>

ui/dr-ui/ui/settings.slint

@@ -1,5 +1,5 @@
 import { Theme } from "theme.slint";
-import { Button, PanelHeading, Label, Value, Caption, Panel, ProgressBar, ActivityRow } from "widgets.slint";
+import { Button, PanelHeading, Label, Value, Caption, Panel, ProgressBar, ActivityRow, ScrollBar } from "widgets.slint";
 import { Segmented, TextRow, Check, SliderRow } from "controls.slint";
 import { ExportImageOptions, ExportFileOptions } from "export.slint";
 import { ScopeChips, ScopeKind } from "presets.slint";
@@ -302,8 +302,11 @@ export component SettingsPage inherits Rectangle {
             }
         }
 
-        Flickable {
+        Rectangle {
                 vertical-stretch: 1;
+            page-flick := Flickable {
+                width: parent.width;
+                height: parent.height;
                 viewport-height: content.preferred-height;
 
                 content := VerticalLayout {
@@ -1029,5 +1032,16 @@ export component SettingsPage inherits Rectangle {
                     }
                 }
             }
+
+            // A bar for a pointer: the page is several screens long, and the bar is
+            // what says so before anything has been scrolled.
+            ScrollBar {
+                x: parent.width - self.width;
+                y: 0px;
+                viewport-y <=> page-flick.viewport-y;
+                viewport-height: page-flick.viewport-height;
+                visible-height: page-flick.height;
+            }
+        }
     }
 }