Add licenses and footer attribution

- LICENSE: MIT for site code, with Serene theme (MIT by isunjn) attribution
- content/LICENSE: CC BY 4.0 for site content
- Footer: add "Built with zola and serene" links

Author: lemonadern

LICENSE

@@ -0,0 +1,48 @@
+MIT License
+
+Copyright (c) 2023-2026 Taishi Naka (lemonadern)
+
+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.
+
+---
+
+This project uses the Serene theme (https://github.com/isunjn/serene),
+which is licensed under the MIT License:
+
+MIT License
+
+Copyright (c) 2021-present isunjn
+
+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.

content/LICENSE

@@ -0,0 +1,17 @@
+Creative Commons Attribution 4.0 International (CC BY 4.0)
+
+Copyright (c) 2023-2026 Taishi Naka (lemonadern)
+
+All content in this directory (articles, texts, and other written materials)
+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
+  - 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.
+
+Full license text: https://creativecommons.org/licenses/by/4.0/

templates/_footer.html

@@ -5,6 +5,8 @@
   <div class="left">
     <div class="copyright">
       {{ config.extra.footer_copyright }}
+      <span>|</span>
+      Built with <a href="https://www.getzola.org/" rel="noreferrer" target="_blank">zola</a> and <a href="https://github.com/isunjn/serene" rel="noreferrer" target="_blank">serene</a>
     </div>
   </div>