fix: source overview blur from parallax shader in scrolling wallpaper mode

The niri overview blur was sourcing from the raw currentWallpaper image,
which is invisible and has no scroll-aware UV cropping in parallax mode.
Now falls through to parallaxLoader.item when active, producing a
correctly framed blur that matches the on-screen wallpaper crop.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: PandorasFox

quickshell/Modules/WallpaperBackground.qml

@@ -970,7 +970,7 @@ Variants {
 
                 sourceComponent: MultiEffect {
                     anchors.fill: parent
-                    source: effectLoader.active ? effectLoader.item : currentWallpaper
+                    source: effectLoader.active ? effectLoader.item : (parallaxLoader.active ? parallaxLoader.item : currentWallpaper)
                     blurEnabled: true
                     blur: 0.8
                     blurMax: 75