feat(cfold): canonicalize custom test layout

tests/mailu/custom/test_health_check.py

@@ -0,0 +1,21 @@
+"""mailu — health/readiness functional test (Phase 2).
+
+SOURCE: no recipe-maintainer corpus exists for mailu (P2 vacuous — see PARITY.md). The nginx front
+serves `/` (301 → /webmail) once the stack is up; this is the canonical "is mailu serving" signal.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
+from harness import http as harness_http  # noqa: E402
+
+
+def test_mailu_front_serves(live_app):
+    url = f"https://{live_app}/"
+    status, _ = harness_http.retry_http_get(
+        url, expect_status=(200, 301, 302), max_wait=120, interval=5
+    )
+    assert status in (200, 301, 302), f"GET {url} HTTP {status} (mailu front not serving)"