theme: stage a scheme and commit it from the header

The Theme page applied a scheme on click, so a stray click reinstalled the
whole theme, and it was the one settings page without the header's
commit point. Clicking now stages the scheme (outlined yellow, "selected"),
and Reset / Apply in the header drop or apply it, as the wallpaper page
does. The applied notice and any failure moved into the SaveBar, and the
sidebar marks the page dirty while a scheme is staged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/desktop/modules/appearance/Udt.qml b/desktop/modules/appearance/Udt.qml
index 98fbba7..9ba609f 100644
--- a/desktop/modules/appearance/Udt.qml
+++ b/desktop/modules/appearance/Udt.qml
@@ -33,6 +33,10 @@ Singleton {
     property bool applying: false
     signal applied(string scheme, bool ok, string message)
 
+    // A scheme picked on the page, staged until Apply, like a wallpaper.
+    property string pending: ""
+    readonly property bool dirty: pending !== "" && pending !== current
+
     // A scheme is two files: <name>.conf holds colours under the scheme's own
     // names, roles-<name>.conf says what each colour is for. Resolving a role
     // means looking its value up as a key in the first file.
@@ -146,6 +150,7 @@ Singleton {
         property string scheme: ""
         onExited: code => {
             root.applying = false;
+            if (code === 0) root.pending = "";
             root.applied(applyProc.scheme, code === 0,
                          code === 0 ? "" : `install.sh exited ${code}, its output is in the steps window`);
         }