fix(packaging): modernize project.license to PEP 639 SPDX string (#38353)

* fix(packaging): modernize project.license to PEP 639 SPDX string

Drops the SetuptoolsDeprecationWarning ('project.license as a TOML table
is deprecated') emitted on every editable build under setuptools>=77 by
switching license = { text = "MIT" } to the SPDX string form plus an
explicit license-files entry. Bumps build-system requires to
setuptools>=77 so an older build backend can't reject the string form.

The warning was non-fatal (builds succeed with it) but surfaces
prominently in install.ps1 build-failure output, where it gets mistaken
for the cause of unrelated Windows build_editable crashes.

* fix(packaging): bound setuptools build requirement per supply-chain policy

Add the <83 upper bound to setuptools>=77.0 so the dep-bounds supply-chain
gate (>=floor,<next_major) passes.

pyproject.toml

@@ -1,5 +1,8 @@
+# PEP 639 SPDX license expression (`license = "MIT"` below) requires
+# setuptools>=77. Keep this floor in lockstep with the `license` form in
+# [project]; an older build backend rejects the string form.
 [build-system]
-requires = ["setuptools>=61.0"]
+requires = ["setuptools>=77.0,<83"]
 build-backend = "setuptools.build_meta"
 
 [project]
@@ -9,7 +12,8 @@ description = "The self-improving AI agent — creates skills from experience, i
 readme = "README.md"
 requires-python = ">=3.11"
 authors = [{ name = "Nous Research" }]
-license = { text = "MIT" }
+license = "MIT"
+license-files = ["LICENSE"]
 dependencies = [
   # Core — every direct dep is exact-pinned to ==X.Y.Z (no ranges).
   # Rationale: ranges allow PyPI to ship a fresh version of a transitive