mod: Ext 8 — quorum over distinct reporters (anti-brigade), 232/232

(:reporters-at-least N) compiles to setof(Br, report(_, Br, Sr), Bsr),
length(Bsr, Nr), Nr >= N — counts distinct reporters, not raw reports.
mod/decide-quorum asserts every report's report/3 fact (base engine scopes to the
decided report) so Prolog can aggregate reporters. One user filing 3 reports stays
:keep under quorum while the count rule escalates. Own suite. +9 tests.

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

lib/mod/conformance.conf

@@ -16,6 +16,7 @@ PRELOADS=(
   lib/mod/explain.sx
   lib/mod/severity.sx
   lib/mod/offenders.sx
+  lib/mod/quorum.sx
   lib/mod/lifecycle.sx
   lib/mod/audit.sx
   lib/mod/api.sx
@@ -34,4 +35,5 @@ SUITES=(
   "lint:lib/mod/tests/lint.sx:(mod-lint-tests-run!)"
   "severity:lib/mod/tests/severity.sx:(mod-severity-tests-run!)"
   "offenders:lib/mod/tests/offenders.sx:(mod-offenders-tests-run!)"
+  "quorum:lib/mod/tests/quorum.sx:(mod-quorum-tests-run!)"
 )