chore: update LICENSE

LICENSE-CONTENT

@@ -0,0 +1,26 @@
+Copyright (C) 2026 Pihkaal <hello@pihkaal.me>
+
+CONTENT LICENSE
+
+All original content in this repository, including images, graphics, and
+assets created by the author, is licensed under the Creative Commons
+Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).
+
+You are free to:
+- Share and adapt these original assets for non-commercial purposes
+
+Under the following terms:
+- Attribution — You must give appropriate credit
+- NonCommercial — You may not use the material for commercial purposes
+
+EXCLUSIONS
+
+This license does NOT apply to:
+- Any Nintendo-related designs, interface elements, or visual likenesses
+- Trademarks, logos, or branding associated with Nintendo
+- Any third-party content not created by the author
+
+Nintendo DS and related assets are property of Nintendo and are used
+here for educational and non-commercial purposes only.
+
+For code licensing, see the LICENSE file (GNU GPL v3).