refactor(timetable): PURPOSE_SUBJECT_FQCN — Artist::class instead of string-literal

The string-literal workaround was added before the Artist model existed
(ARCH-09 prerequisite). With the model now landed (RFC-TIMETABLE v0.2
Session 1), resolve to Artist::class directly so morph-map registration
matches the rest of the registry. MorphMapAlignmentTest still green.

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

api/app/Providers/AppServiceProvider.php

@@ -16,6 +16,7 @@ use App\Listeners\FormBuilder\ApplyBindingsOnFormSectionSubmitted;
 use App\Listeners\FormBuilder\ApplyBindingsOnFormSubmit;
 use App\Listeners\FormBuilder\SyncTagPickerSelectionsOnSubmit;
 use App\Listeners\FormBuilder\TriggerPersonIdentityMatchOnFormSubmit;
+use App\Models\Artist;
 use App\Models\Company;
 use App\Models\CrowdList;
 use App\Models\CrowdType;
@@ -72,17 +73,16 @@ class AppServiceProvider extends ServiceProvider
     /**
      * FQCN lookup for every `subject_type` alias that PurposeRegistry may
      * return. Single source of truth for domain-subject → model mapping,
-     * consumed by the morph-map build in boot(). The `artist` class is
-     * declared as a string because the Artist model is not yet landed;
-     * it is safe to register the morph alias (lazily resolved).
+     * consumed by the morph-map build in boot(). `artist` resolves to
+     * `App\Models\Artist` (introduced 2026-05, RFC-TIMETABLE Session 1).
      *
-     * @var array<string, class-string|string>
+     * @var array<string, class-string>
      */
     private const PURPOSE_SUBJECT_FQCN = [
         'person' => Person::class,
         'user' => User::class,
         'company' => Company::class,
-        'artist' => 'App\\Models\\Artist',
+        'artist' => Artist::class,
     ];
 
     public function register(): void