Fix sdist LICENSE inclusion for PyPI release

[pratyush618]

Summary

• Add license = \"MIT\" and license-files = [\"LICENSE\"] to [project] in pyproject.toml so maturin's sdist actually includes the LICENSE file. PyPI rejected the 0.1.0 sdist with 400 License-File LICENSE does not exist in distribution file dagron-0.1.0.tar.gz at dagron-0.1.0/LICENSE.
• Add description / license / repository / keywords / categories to crates/dagron-core/Cargo.toml for crates.io readiness.

Context

The 0.1.0 wheels uploaded successfully (run 25605917409); only the sdist upload returned 400. Verified locally that the sdist now contains dagron-0.1.0/LICENSE and PKG-INFO declares License-Expression: MIT + License-File: LICENSE.

Test plan

• Rebuilt sdist locally with maturin sdist — LICENSE now present in tarball
• After merge: re-cut the 0.1.0 release from the web UI; the publish workflow's skip-existing: true will skip already-uploaded wheels and upload the fixed sdist