chore(licence): normalise to MPL-2.0 (code) + CC-BY-SA-4.0 (docs)

- LICENSES/ = {MPL-2.0.txt, CC-BY-SA-4.0.txt}; root LICENSE = verbatim MPL-2.0 (GitHub display)
- SPDX: code -> MPL-2.0, docs (.md/.adoc) -> CC-BY-SA-4.0; metadata/badge fixes; vendored untouched

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.claude/CLAUDE.md

@@ -1,5 +1,5 @@
 <!--
-SPDX-License-Identifier: MPL-2.0
+SPDX-License-Identifier: CC-BY-SA-4.0
 Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 -->
 # Skein.jl — Project Instructions
@@ -66,7 +66,7 @@ julia --project=. -e 'using Pkg; Pkg.resolve()'
 ## Critical Invariants
 
 <!-- REUSE-IgnoreStart -->
-- All files must have `SPDX-License-Identifier: MPL-2.0` header
+- All files must have `SPDX-License-Identifier: CC-BY-SA-4.0` header
 <!-- REUSE-IgnoreEnd -->
 - SCM files in `.machine_readable/` ONLY
 - Tests must pass before any commit

.github/workflows/governance.yml

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: PMPL-1.0-or-later
+# SPDX-License-Identifier: MPL-2.0
 name: Governance
 
 on:

.github/workflows/hypatia-scan.yml

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: PMPL-1.0-or-later
+# SPDX-License-Identifier: MPL-2.0
 name: Hypatia Security Scan
 
 on:

.github/workflows/workflow-linter.yml

@@ -38,7 +38,7 @@ jobs:
             fi
           done
           if [ $failed -eq 1 ]; then
-            echo "Add '# SPDX-License-Identifier: PMPL-1.0' as first line"
+            echo "Add '# SPDX-License-Identifier: MPL-2.0' as first line"
             exit 1
           fi
           echo "All workflows have SPDX headers"

.machine_readable/6a2/README.adoc

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: CC-BY-SA-4.0
 // Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 # A2ML 6a2 Directory
 

.machine_readable/6a2/anchor/README.adoc

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: CC-BY-SA-4.0
 // Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
 # A2ML Anchor Directory
 

.machine_readable/bot_directives/README.adoc

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: CC-BY-SA-4.0
 // Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
 = Agent Instructions
 :toc: preamble

ABI-FFI-README.md

@@ -1,4 +1,4 @@
-<!-- SPDX-License-Identifier: MPL-2.0 -->
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
 <!-- Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk> -->
 
 # Skein.jl ABI/FFI Layer

CHANGELOG.md

@@ -1,4 +1,4 @@
-<!-- SPDX-License-Identifier: MPL-2.0 -->
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
 <!-- Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk> -->
 
 # Changelog — Skein.jl

CODE_OF_CONDUCT.md

@@ -1,4 +1,4 @@
-<!-- SPDX-License-Identifier: MPL-2.0 -->
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
 <!-- Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk> -->
 
 # Code of Conduct