license: switch from GPL-3.0 to MIT OR Apache-2.0 dual license

Companies integrating security tooling into proprietary stacks are
blocked by GPL copyleft. MIT/Apache-2.0 dual licensing matches the
convention used by the Rust ecosystem (tokio, axum, serde, etc.) and
removes all adoption friction for commercial users.

- Add LICENSE-MIT
- Add LICENSE-APACHE
- Update LICENSE.md to dual-license declaration
- Add [workspace.package] license field to Cargo.toml

Cargo.toml

@@ -6,3 +6,6 @@ members = [
     "server",
     "wasm"
 ]
+
+[workspace.package]
+license = "MIT OR Apache-2.0"