Gateway Audit Events

Sprint G adds redacted audit-style event records for the local mock runtime.

Events cover request lifecycle milestones such as request received, request validated, route planned, mock provider started/completed, stream started/chunk/completed, request completed/failed, auth failed, and runtime start/stop.

Event names are intentionally precise. They do not claim external provider calls, live fallback, retry execution, or production routing.

Events are stored in memory only and are bounded by collector configuration.