chore: fix license headers to PMPL-1.0-or-later

- Update SPDX identifiers from AGPL to PMPL
- Ensure LICENSE file uses PMPL-1.0-or-later
- Maintain consistency with palimpsest-license repo

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Your Name

.github/workflows/ci.yml

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
 name: CI/CD Pipeline
 
 on:

.github/workflows/jekyll-gh-pages.yml

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
 # Sample workflow for building and deploying a Jekyll site to GitHub Pages
 name: Deploy Jekyll with GitHub Pages dependencies preinstalled
 

.github/workflows/php-security.yml

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
 name: PHP Security Check
 on: [push, pull_request]
 jobs:

.github/workflows/rescript-deno-ci.yml

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
 name: ReScript/Deno CI
 on: [push, pull_request]