Relicense to MIT (v2.7.13)

The project's only runtime dependency is PyUSB (BSD-3-Clause) and it bundles
no third-party code (the PWA's DES/3DES is written from the FIPS 46-3 tables,
AES uses WebCrypto, the decoders come from the ISO 7816/ETSI/3GPP specs), so
nothing forced GPL; the GPL-2.0-or-later declaration is replaced with MIT.

- LICENSE: the MIT text, Copyright (c) 2026 Anton Troshin.
- pyproject: license = "MIT" + license-files = ["LICENSE"] (PEP 639), and the
  build requirement moves to setuptools>=77 for the SPDX form.  The wheel now
  carries dist-info/licenses/LICENSE and License-Expression: MIT, the sdist
  and the runtime zip carry LICENSE at the top.
- READMEs (EN/RU): a License section (original decoders/DES implementation,
  PyUSB as the only runtime dependency).
- tests: the packaging test pins the MIT declaration and the LICENSE text;
  the release-zip test requires LICENSE in the archive.
- version 2.7.13; SW cache v95.

Copies published before this tag (v2.7.10-v2.7.12) remain under the license
they were released with.

.github/release-notes.md

@@ -18,3 +18,5 @@ is the runtime tree only (packages, PWA, launchers, docs — no tests, no git):
 extract it anywhere and run `start.bat` (Windows) or `./start.sh`
 (Linux/macOS).  Python 3 has to be on `PATH`; `pip install pyusb` is only
 needed for direct SIMtrace2 capture.
+
+The project is MIT-licensed (see `LICENSE`).