feat(cfold): canonicalize custom test layout

tests/plausible/PARITY.md

@@ -20,10 +20,10 @@ a true readiness gate. `DEPLOY_TIMEOUT` / `HTTP_TIMEOUT` are widened to 1200s to
 ClickHouse + migrations init.
 
 ## P3 — Recipe-specific functional tests
-- `functional/test_health_check.py`
+- `custom/test_health_check.py`
   - `test_plausible_root_serves` — GET `/api/health` → 200, proving ClickHouse + postgres + the
     sites_cache are all up (plausible's self-reported backend readiness; not a Traefik fallback).
-- `functional/test_event_tracking.py` — **§4.3 prescribed "track a test event, query it back"**, the
+- `custom/test_event_tracking.py` — **§4.3 prescribed "track a test event, query it back"**, the
   app's primary object. Both tests register a site row in the metadata postgres (plausible's
   `sites_cache` drops events for unregistered domains — empirically confirmed), POST to the public
   `/api/event` ingestion endpoint with a browser User-Agent (plausible drops bot/library UAs), then