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.

THIRD_PARTY_NOTICES.md

@@ -0,0 +1,21 @@
+<!--
+SPDX-FileCopyrightText: 2026 Paul Schoeneck
+
+SPDX-License-Identifier: AGPL-3.0-only AND LicenseRef-KIBU-Additional-Terms
+-->
+
+# Third-party notices
+
+KIBU's license applies to original KIBU material, not to third-party packages.
+Dependencies retain their licenses, copyright notices and other requirements.
+Their license metadata is recorded in `package-lock.json`; their complete
+notices are distributed in their installed package directories.
+
+The generated `next-env.d.ts` file originates from Next.js:
+Copyright (c) 2025 Vercel, Inc., MIT License. See [MIT](LICENSES/MIT.txt).
+Do not replace its generated contents with a KIBU copyright header.
+
+Before distributing a bundled build, container, or dependency directory, retain
+the applicable third-party license and notice files for the exact shipped
+versions, including transitive dependencies. REUSE lint checks repository file
+annotations; it is not an audit of installed dependencies or deployment bundles.