Beacon Primitives

This phase adds the small integration pieces Beacon needs from the

existing runtime without introducing a second transport stack.

Named-beacon notifications

internal/notify.NotifyEvent now has optional beacon_id,

sessionid, and artifactref fields so webhook payloads can target

or explain Beacon-specific operator work.

internal/beacon/review.Envelope is the minimal structured shape for an

offline review request. It binds:

That shape is intentionally small so later Beacon trust handlers can

emit it directly into notifications or artifact-linked workflows.