Apply pending shell theme after background polling

shell/plugins/background/Background.qml

@@ -70,7 +70,9 @@ Item {
   }
 
   function applyPendingTheme() {
-    if (pendingThemeVersion !== backgroundVersion) return
+    // Background polling can advance backgroundVersion while a theme switch is
+    // pending; the latest theme payload should still apply.
+    if (pendingThemeVersion < 0) return
     pendingThemeFallbackTimer.stop()
     Color.loadColors(pendingColorsRaw)
     // Color.loadShell also refreshes Style so the type scale flips with the

test/shell.d/background-test.sh

@@ -14,7 +14,8 @@ assert(
 assert(
   backgroundQml.includes('pendingThemeFallbackTimer.restart()') &&
     backgroundQml.includes('pendingThemeFallbackTimer.stop()') &&
-    backgroundQml.includes('id: pendingThemeFallbackTimer'),
+    backgroundQml.includes('id: pendingThemeFallbackTimer') &&
+    !backgroundQml.includes('pendingThemeVersion !== backgroundVersion'),
   'background theme transition applies pending colors even if image reveal stalls'
 )
 JS