feat: nixppuccin wallpaper

Signed-off-by: jolheiser <john.olheiser@gmail.com>

.gitattributes

@@ -1 +1,5 @@
+# Age
 apps/gui/firefox/work.nix filter=git-age diff=git-age
+
+# Git LFS
+*.png filter=lfs diff=lfs merge=lfs -text

apps/gui/default.nix

@@ -34,4 +34,7 @@
       jolheiser.nur.tmpl
     ];
   };
+  dconf.settings."org/cinnamon/desktop/background" = {
+    picture-uri = "file://${./wallpaper/nixppuccin.png}";
+  };
 }