mod: Ext 16 — ActivityPub-shaped decision export, 350/350

mod/decision->activity maps a decision to a moderation verb (remove→Delete,
ban→Block, hide/escalate→Flag, keep→no activity) shaped like an AP activity,
preserving the precise action. mod/decisions->activities batch-exports dropping
keeps. With wire (Ext 14) + fed trust (Phase 4) the federated moderation path is
end-to-end: decide → activity/wire → peer → trust-gate → apply. +17 tests.

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

lib/mod/conformance.conf

@@ -23,6 +23,7 @@ PRELOADS=(
   lib/mod/temporal.sx
   lib/mod/sla.sx
   lib/mod/wire.sx
+  lib/mod/activity.sx
   lib/mod/lifecycle.sx
   lib/mod/audit.sx
   lib/mod/api.sx
@@ -49,4 +50,5 @@ SUITES=(
   "sla:lib/mod/tests/sla.sx:(mod-sla-tests-run!)"
   "wire:lib/mod/tests/wire.sx:(mod-wire-tests-run!)"
   "disjunction:lib/mod/tests/disjunction.sx:(mod-disjunction-tests-run!)"
+  "activity:lib/mod/tests/activity.sx:(mod-activity-tests-run!)"
 )