Add CC BY 4.0 LICENSE file

LICENSE

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+Creative Commons Attribution 4.0 International License (CC BY 4.0)
+
+Copyright (c) 2026 Alexander Wirth
+
+This work is licensed under the Creative Commons Attribution 4.0 
+International License.
+
+You are free to:
+
+  Share — copy and redistribute the material in any medium or format
+  for any purpose, even commercially.
+
+  Adapt — remix, transform, and build upon the material for any 
+  purpose, even commercially.
+
+Under the following terms:
+
+  Attribution — You must give appropriate credit, provide a link to 
+  the license, and indicate if changes were made. You may do so in 
+  any reasonable manner, but not in any way that suggests the licensor 
+  endorses you or your use.
+
+  No additional restrictions — You may not apply legal terms or 
+  technological measures that legally restrict others from doing 
+  anything the license permits.
+
+Full license text: https://creativecommons.org/licenses/by/4.0/legalcode