fix: use license-file for crates.io compatibility

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

Cargo.toml

@@ -5,7 +5,7 @@ version = "0.1.0"
 edition = "2024"
 authors = ["Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>"]
 description = "Compile annotated array operations to GPU kernels via Futhark without touching CUDA"
-license = "PMPL-1.0-or-later"
+license-file = "LICENSE"
 repository = "https://github.com/hyperpolymath/futharkiser"
 keywords = ["futhark", "gpu", "cuda", "opencl", "acceleration"]
 categories = ["command-line-utilities", "development-tools"]