Add nord theme with license header, update all theme files with license

ash.css

@@ -1,4 +1,8 @@
-/* Generic color system - simple to customize for other themes.
+/* Ash palette by zink (this project)
+ * Original: https://git.familie-zink.org/zink/omarchy-ash-theme
+ * License: See repository LICENSE
+ *
+ * Generic color system - simple to customize for other themes.
    Each color has light/dark variants interpolated from the base color. */
 
 :root {