Tenant-scoped PubSub fan-out for reviewer dashboard trace events.

Use this module when runtime telemetry needs to reach /scoria reviewer pages without crossing tenant boundaries. It publishes trace headers, trace spans, streaming trace deltas, HITL approval requests, and approval decisions to scoria:runs:{tenant_id}.

Tracks seen trace_id values per BEAM node in ETS (:scoria_observe_reviewer_broadcast_trace_seen) so {:trace_opened, _} is emitted only on the first span stop for a trace on this node. Missing tenant_id drops broadcast fail-closed with a debug log; there is no global topic fallback.

See guides/reviewer-verification.md for reviewer trace verification and guides/ownership-boundary.md for the host-owned tenant-scope boundary.