Apply shell theme if background reveal stalls

shell/plugins/background/Background.qml

@@ -66,10 +66,12 @@ Item {
     pendingColorsRaw = Util.decodeBase64(colorsB64)
     pendingShellRaw = Util.decodeBase64(shellB64)
     pendingThemeVersion = backgroundVersion
+    pendingThemeFallbackTimer.restart()
   }
 
   function applyPendingTheme() {
     if (pendingThemeVersion !== backgroundVersion) return
+    pendingThemeFallbackTimer.stop()
     Color.loadColors(pendingColorsRaw)
     // Color.loadShell also refreshes Style so the type scale flips with the
     // background reveal instead of waiting for a separate reload path.
@@ -154,6 +156,13 @@ Item {
     onTriggered: root.refreshBackground()
   }
 
+  Timer {
+    id: pendingThemeFallbackTimer
+    interval: 300
+    repeat: false
+    onTriggered: root.applyPendingTheme()
+  }
+
   NumberAnimation {
     id: revealAnimation
     target: root