chore(licence): normalise to MPL-2.0 + CC-BY-SA-4.0 (canonical pair) (#68)

Estate licence normalisation. LICENSES/={MPL-2.0,CC-BY-SA-4.0}; root
LICENSE=verbatim MPL-2.0 (GitHub display); code->MPL-2.0,
docs(.md/.adoc)->CC-BY-SA-4.0; vendored untouched. Residual mentions
(mostly legitimate anti-AGPL rules): 27. Manual-review licence PR.

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

Author: hyperpolymath

.devcontainer/README.adoc

@@ -357,7 +357,7 @@ Exhibit A - Source Code Form License Notice
 
   This Source Code Form is subject to the terms of the Mozilla Public
   License, v. 2.0. If a copy of the MPL was not distributed with this
-  file, You can obtain one at https://mozilla.org/MPL/2.0/.
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 If it is not possible or desirable to put the notice in a particular
 file, then You may include the notice in a location (such as a LICENSE