chore(license): align Cargo.toml license to LICENSE (MPL-2.0) (#52)

Closes #51.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

Cargo.toml

@@ -7,7 +7,7 @@ resolver = "2"
 
 [workspace.package]
 edition = "2021"
-license = "MIT OR MPL-2.0"
+license = "MPL-2.0"
 repository = "https://github.com/hyperpolymath/januskey"
 authors = ["Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>"]