Add licensing information and update README for KIBU

- Introduced additional terms under Section 7 of the GNU AGPL v3 for KIBU, including attribution, marking of modified versions, and trademark usage.
- Added MIT License file for clarity on licensing options.
- Updated README.md to reflect the new licensing terms, including detailed usage rights and obligations.
- Created REUSE.toml for SPDX compliance and license annotations.
- Added THIRD_PARTY_NOTICES.md to clarify third-party dependencies and their licenses.
- Updated various source files and scripts to include SPDX headers for copyright and licensing.
- Enhanced footer in layout to display licensing information and project link.
- Implemented a new license page to present the AGPL and additional terms clearly.

LICENSE

@@ -0,0 +1,18 @@
+KIBU
+Copyright (C) 2026 Paul Schoeneck
+
+SPDX-License-Identifier: AGPL-3.0-only AND LicenseRef-KIBU-Additional-Terms
+
+KIBU is licensed under the GNU Affero General Public License, version 3
+only (not "or any later version"), with the additional terms permitted
+by Section 7 set out in LICENSES/LicenseRef-KIBU-Additional-Terms.txt.
+
+The complete, unmodified AGPL v3 text is in LICENSES/AGPL-3.0-only.txt.
+Both documents form the applicable licensing terms for original KIBU
+material. Third-party components retain their own licenses and notices.
+
+This program is distributed WITHOUT ANY WARRANTY; without even the
+implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+See the GNU Affero General Public License for details.
+
+Original project: https://git.voidcube.de/pixo2000/KIBU