fix(timetable): config-flag observer + cleaner idempotency_key

OrganisationObserver was gated on app()->runningUnitTests() — replaced
with config('artist_advance.bootstrap_on_org_create') (default true,
phpunit.xml overrides to false). Behaviour identical, but the seam is
explicit and removable. Tracked for full convergence by new BACKLOG
entry TECH-OBSERVER-TEST-CONVERGENCE — productiegedrag = testgedrag,
geen branching, na test-cleanup.

idempotency_key for the engagement-scoped draft simplified from
'aa-' + sha1(engagement_id)[0:27] to 'aa:' + engagement_id (29 chars,
fits varchar(30)). Same uniqueness guarantee, recognisable shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/Http/Controllers/Api/V1/Portal/EngagementPortalController.php

@@ -257,16 +257,13 @@ final class EngagementPortalController extends Controller
         // Pass event_id via the context bag — the schema is org-owned (not
         // event-owned) and this route has no {event} parameter for the
         // FormSubmissionObserver fallback. ARCH-FORM-BUILDER §17.3 footnote.
-        // idempotency_key column is varchar(30); a SHA-1 hex digest fits in
-        // 28 chars and uniquely keys "one draft per (schema, engagement)".
-        $key = 'aa-'.substr(hash('sha1', (string) $resolved->engagement->id), 0, 27);
-
+        // idempotency_key column is varchar(30); 'aa:' + 26-char ULID fits.
         return $this->submissionService->createDraft(
             schema: $schema,
             subject: $resolved->subject,
             submitter: null,
             context: [
-                'idempotency_key' => $key,
+                'idempotency_key' => 'aa:'.$resolved->engagement->id,
                 'event_id' => $resolved->eventId,
             ],
         );