chore(license): declare MIT on the crates (open-source Phase 4a A4)

The repo ships an MIT LICENSE and the README carries an MIT badge, but the
crates themselves declared no license, so `cargo metadata`, packaging and any
downstream mirror saw "license: null". Adds [workspace.package] license = "MIT"
and inherits it in all five members via license.workspace = true. Verified with
cargo metadata: all five now report MIT.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/security/Cargo.toml

@@ -2,6 +2,7 @@
 name = "archipelago-security"
 version = "0.1.0"
 edition = "2021"
+license.workspace = true
 
 [dependencies]
 tokio = { version = "1", features = ["full"] }