assets: adds license notices to all files

assets/res/arctica.css

@@ -1,4 +1,16 @@
-/* martian theme */
+/*
+ * Copyright (c) 2022 Sasha Koshka <sashakoshka@tebibyte.media>
+ * SPDX-License-Identifier: FSFAP
+ *
+ * This file is part of Mintee.
+ *
+ * Copying and distribution of this file, with or without modification, are
+ * permitted in any medium without royalty provided the copyright notice and
+ * this notice are preserved.  This file is offered as-is, without any
+ * warranty.
+ */
+
+/* arctica theme */
 :root {
 	--glass:             url("frost.webp"), #24293370;
 	--background:        #242933;