feat(timetable): ArtistAdvanceDefault seeder + bootstrap

Seeds 5 default sections per RFC v0.2 D15 (General Info, Contacts,
Production, Technical Rider, Hospitality) on a per-organisation
artist_advance FormSchema with section_level_submit=true. Each
section ships with 3-4 illustrative form_fields; organisations
customise via the FormBuilder UI later.

Wired into org-creation via the new OrganisationObserver so new
tenants receive the schema automatically. Existing orgs get
coverage via the new artist:seed-advance-default artisan command
(idempotent — orgs that already own a schema are skipped).

Note: introduces a new production-grade default-seeder convention.
Prior FormBuilder defaults were dev-only via FormBuilderDevSeeder
called from DevSeeder::run(). This is the first non-dev path.

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

api/app/Observers/OrganisationObserver.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Observers;
+
+use App\FormBuilder\Defaults\ArtistAdvanceDefault;
+use App\Models\Organisation;
+
+/**
+ * Bootstrap an organisation's domain defaults on creation.
+ *
+ * Currently provisions the artist_advance FormSchema (RFC-TIMETABLE
+ * v0.2 D15) so new tenants can use the artist portal flow without a
+ * separate manual step. Existing organisations get the same coverage
+ * via the `artist:seed-advance-default` artisan command.
+ *
+ * The default seeder is idempotent — if the org already owns an
+ * artist_advance schema, the call is a no-op. Safe to re-run.
+ */
+final class OrganisationObserver
+{
+    public function created(Organisation $organisation): void
+    {
+        ArtistAdvanceDefault::seedFor($organisation);
+    }
+}