[security] authorize(ns) is pub with no gate consult — multi-actor policy bypass

[ohdearquant]

Integration codex security review S-1.

KhiveRuntime::authorize(ns) at crates/khive-runtime/src/runtime.rs:359 is pub and mints a NamespaceToken for any namespace with NO gate consultation. When a real Gate impl ships (replacing AllowAllGate), this bypasses the policy decision the moment something like build_edge/link_many calls authorize() internally.

Multi-actor deployments need authorize() to consult the gate. OSS single-user is unaffected.