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/Providers/AppServiceProvider.php

@@ -153,6 +153,7 @@ class AppServiceProvider extends ServiceProvider
 
         Person::observe(PersonObserver::class);
         User::observe(UserObserver::class);
+        Organisation::observe(\App\Observers\OrganisationObserver::class);
         FormValue::observe(FormValueObserver::class);
         \App\Models\FormBuilder\FormSubmission::observe(FormSubmissionObserver::class);