docs: add licence, contributing, and third-party notices

LICENCE

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+MIT License
+
+Copyright (c) 2026 OnixByte
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+---
+CC-BY-4.0
+
+Copyright (c) 2026 OnixByte
+
+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.
+
+The licensor cannot revoke these freedoms as long as you follow the license terms.
+
+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.
+
+NOTICES
+
+You do not have to comply with the license for elements of the material in the public domain or
+where your use is permitted by an applicable exception or limitation.
+
+No warranties are given. The license may not give you all of the permissions necessary for your
+intended use. For example, other rights such as publicity, privacy, or moral rights may limit
+how you use the material.
+
+---
+
+This project applies a dual-licensing model:
+
+- Code (source code, build scripts, theme, configuration) is licensed under the MIT License (above).
+- Content (blog posts, documentation articles, and other written content under docs/) is licensed under the Creative Commons Attribution 4.0 International License (CC-BY-4.0).
+
+To view a copy of CC-BY-4.0, visit https://creativecommons.org/licenses/by/4.0/