mod: Phase 4 — federation (trust, sharing, revocation), 132/132 — roadmap done

Cross-instance reports ingest into the local registry with origin tags; the
engine decides them unchanged. Decision sharing pushes to a mock fed-sx outbox
(mod/fed-send! is the transport seam). Trust is advisory by default: a peer's
decision binds locally only under (mod/trusted? peer :mod), else it lands in the
advisory log unapplied. Revocation composes with the Phase-2 proof model —
fed-revoke-if-invalidated re-runs the engine and undoes moderation only when the
action no longer holds (exoneration flips hide→keep → revoked + origin notified).
+26 fed tests. Full mod-on-sx roadmap complete.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/mod/scoreboard.md

@@ -1,9 +1,10 @@
 # mod scoreboard
 
-**106 / 106 passing** (0 failure(s)).
+**132 / 132 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
 | decide | 31 | 31 | ok |
 | audit | 29 | 29 | ok |
 | escalation | 46 | 46 | ok |
+| fed | 26 | 26 | ok |