Fix CI Nix installation and adopt MIT license

- Run CI jobs in `node:22-bookworm` container, install sudo and disable
  KVM for the Nix installer.
- Replace CC0 with the MIT license and add `license = "MIT"` to
  Cargo.toml.
- Update README and documentation (CODE_MAP, PROGRESS, TESTING) to
  reflect the new license and CI changes.

Cargo.toml

@@ -3,6 +3,7 @@ name = "war_in_tunnels"
 version = "0.1.0"
 edition = "2024"
 rust-version = "1.88"
+license = "MIT"
 
 [lints.rust]
 unused_must_use = "deny"