test(gate): make 5× the canonical gate, drop 20x naming

Rename run-20x.sh → run-gate.sh, default ARCHY_ITERATIONS 20→5, and scrub
20× references across CLAUDE.md, the master plan, TESTING.md, app-registry
status, the orchestrator/config doc-comments, and the bats suites. Also add
a minimal fail() helper to mempool.bats so guard failures report cleanly.

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

scripts/create-release.sh

@@ -80,7 +80,7 @@ fi
 # runs the release gate harness (cargo fmt/check, catalog drift, vitest, and
 # the focused cargo suites — incl. the receive/port-drift/secret regressions).
 # Skipped on --dry-run, or set SKIP_RELEASE_TESTS=1 to bypass in an emergency.
-# The lifecycle bats harness (tests/lifecycle/run-20x.sh) still runs separately
+# The lifecycle bats harness (tests/lifecycle/run-gate.sh) still runs separately
 # against live nodes — see tests/lifecycle/TESTING.md.
 if ! $DRY_RUN; then
     if [ "${SKIP_RELEASE_TESTS:-0}" = "1" ]; then