docs: update license to PMPL-1.0-or-later + CC-BY-SA-4.0

- Update README: Code is under PMPL-1.0-or-later and docs are under CC-BY-SA-4.0
- Update LICENSE: Add dual licensing header, fix SPDX identifier
- Add LICENSES directory with PMPL-1.0-or-later.txt and CC-BY-SA-4.0.txt

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Author: hyperpolymath

bots/the-hotchocolabot/LICENSE

@@ -1,4 +1,11 @@
-SPDX-License-Identifier: MPL-2.0
+Code is licensed under Palimpsest Public License Version 1.0 (PMPL-1.0-or-later).
+Documentation is licensed under Creative Commons Attribution-ShareAlike 4.0 International (CC-BY-SA-4.0).
+
+See LICENSES/ directory for full license texts.
+
+---
+
+SPDX-License-Identifier: PMPL-1.0-or-later
 SPDX-FileCopyrightText: 2024-2025 Palimpsest Stewardship Council
 
 ================================================================================