licence(#7): normalise PMPL-1.0 -> PMPL-1.0-or-later (owner carve-out, SPDX-only) (#5)

Not a relicence; owner-sanctioned standards LICENCE-POLICY A8(1).
Refs LICENCE-DEBT-LEDGER-2026-05-18.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/workflow-linter.yml

@@ -37,7 +37,7 @@ jobs:
             fi
           done
           if [ $failed -eq 1 ]; then
-            echo "Add '# SPDX-License-Identifier: PMPL-1.0' as first line"
+            echo "Add '# SPDX-License-Identifier: PMPL-1.0-or-later' as first line"
             exit 1
           fi
           echo "All workflows have SPDX headers"