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>

CLAUDE.md

@@ -42,10 +42,9 @@ Detailed sub-plans (all linked from the master):
 
 ## Production test gate (definition of done)
 
-`tests/lifecycle/run-20x.sh` green across install / UI / stop / start / restart /
+`tests/lifecycle/run-gate.sh` green across install / UI / stop / start / restart /
 reinstall / reboot-survive / archipelago-restart-survive / uninstall — **5× on
-.228** (`ARCHY_ITERATIONS=5`; temporarily reduced from 20× — restore to 20× before
-the final ship). **Run the gate ON the node** (it uses local podman/systemctl/bitcoin
+.228** (`ARCHY_ITERATIONS=5`). **Run the gate ON the node** (it uses local podman/systemctl/bitcoin
 probes), not via RPC from another host. Until green, the master plan is the priority.
 **Multinode testing (.198 + the rest of the fleet) is a SEPARATE plan** —
 `docs/multinode-testing-plan.md` — not part of this single-node gate criterion.