assets: adds license notices to all files

assets/res/mint.css

@@ -1,3 +1,16 @@
+/*
+ * Copyright (c) 2022, 2025 Sasha Koshka <sashakoshka@tebibyte.media>
+ * Copyright (c) 2026 Emma Tebibyte <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.
+ */
+
 @import url("/res/mint-dark.css") (prefers-color-scheme: dark);
 
 @media (prefers-color-scheme: light) {