Security primitives for Agent Assembly.

This crate owns the credential-detection scanner, the redaction primitives, and the audit-normalization types relied on by the trusted enforcement layers (aa-runtime, aa-gateway, aa-proxy).

It is deliberately a leaf crate: it does not depend on aa-core, so security authority comes from where a primitive runs, not from the core domain crate. The primitives are progressively moved here from aa-core (see AAASM-2567); aa-core keeps temporary pub use re-exports for migration compatibility.

Feature Flags

• serde: enables Serialize/Deserialize derives on the public types.