Add MIT licence

Declared with the PEP 639 license / license-files fields, so the text ships in
the wheel and the image rather than only the repository. Records the terms of
the two things this repository deliberately does not contain: Boxsim, which is
Visaton freeware and is never redistributed, and kicad-visaton-lib, which is
CC-BY-SA-4.0 and is copied into any image built by tools/build-image.sh.

Verified: pip install exposes License-Expression MIT and packages the text as
dist-info/licenses/LICENSE, both on the host and in the image.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools>=68"]
+requires = ["setuptools>=77"]
 build-backend = "setuptools.build_meta"
 
 [project]
@@ -8,7 +8,8 @@ version = "0.1.0"
 description = "Read Boxsim loudspeaker projects and generate KiCad projects from their crossovers"
 readme = "README.md"
 requires-python = ">=3.11"
-license = { text = "MIT" }
+license = "MIT"
+license-files = ["LICENSE"]
 authors = [{ name = "Marco Grätsch", email = "magdev3.0@gmail.com" }]
 keywords = ["boxsim", "visaton", "kicad", "loudspeaker", "crossover"]
 dependencies = []