fix(desktop): follow swaylock config move, use blurred wallpaper

The config source is defaults/etc/swaylock/config now. The tmpfiles seed
stays: nixpkgs leaves meson's sysconfdir at $out/etc, so the
/etc/swaylock/config that Arch owns is never read here.

modules/desktop.nix

@@ -16,6 +16,7 @@ let
   '';
 
   wallpaper = "${moonarchSrc}/defaults/backgrounds/wallpaper.jpg";
+  wallpaperBlur = "${moonarchSrc}/defaults/backgrounds/wallpaper-blur.jpg";
 
   # waypaper's config points at /usr/share/moonarch/wallpaper.jpg, which does
   # not exist here. Generated with the store path instead of copied verbatim.
@@ -27,10 +28,12 @@ let
   # Same treatment for swaylock's wallpaper path. swaylock searches
   # ~/.swaylock/config, $XDG_CONFIG_HOME/swaylock/config and
   # SYSCONFDIR/swaylock/config — and its sysconfdir is inside the store here,
-  # so the home copy seeded below is the only one it ever reads.
+  # so the home copy seeded below is the only one it ever reads. On Arch the
+  # same file ships to /etc/swaylock/config, which is why it lives in
+  # defaults/etc/ rather than defaults/xdg/.
   swaylockConfig = pkgs.runCommand "swaylock-config" { } ''
-    substitute ${xdg}/swaylock/config "$out" \
+    substitute ${etc}/swaylock/config "$out" \
-      --replace-fail /usr/share/moonarch/wallpaper.jpg ${wallpaper}
+      --replace-fail /usr/share/moonarch/wallpaper-blur.jpg ${wallpaperBlur}
   '';
 in
 {