fix(ci): add SPDX-License-Identifier header to LICENSE (#31)

Clears the Governance 'Licence consistency' gate (check-licence-consistency.sh requires an SPDX-License-Identifier on LICENSE's first lines). LICENSE is the verbatim MPL-2.0 text; this adds the matching identifier + copyright. Sole-owner repo -> MPL-2.0 per estate policy. (tropical: also adds a license field to Project.toml.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Claude-Session: https://claude.ai/code/session_019awZjBD1qx61tvmEuEKNpn

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

LICENSE

@@ -1,3 +1,6 @@
+SPDX-License-Identifier: MPL-2.0
+SPDX-FileCopyrightText: 2024-2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+
 Mozilla Public License Version 2.0
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