feat(cfold): canonicalize custom test layout

tests/mattermost-lts/PARITY.md

@@ -12,14 +12,14 @@ tiers run by default (the Phase-1e invariant: no overlay ⇒ generic runs). The
 postgres in-compose (no external dep), so no dependency resolution is needed.
 
 ## P3 — Recipe-specific functional tests (≥2 separate characteristic tests)
-1. `functional/test_create_message.py::test_create_message_roundtrip` — **§4.3 create-an-object +
+1. `custom/test_create_message.py::test_create_message_roundtrip` — **§4.3 create-an-object +
    read-it-back**: first user (system admin) → login → create team → create channel → POST a unique
    marker message → GET it back by id → assert the text round-trips.
-2. `functional/test_multiuser_message.py::test_second_user_reads_first_users_message` — the defining
+2. `custom/test_multiuser_message.py::test_second_user_reads_first_users_message` — the defining
    **team-chat** behaviour (distinct code path: membership + ACL + cross-user delivery): user_a posts a
    unique marker; a SECOND user (created via admin API, added to team+channel) logs in with its own
    session and GETs the channel posts → asserts it sees user_a's message. Not a self read-back.
-- `functional/test_health_check.py` — `test_root_serves` (`/` 200/302) + `test_system_ping_ok`
+- `custom/test_health_check.py` — `test_root_serves` (`/` 200/302) + `test_system_ping_ok`
   (`/api/v4/system/ping` → `{"status":"OK"}`, API liveness). Supporting health/liveness, not counted
   toward the P3 ≥2 floor.