feat(form-builder): introduce purpose registry and definition value object

Lands the v1.0 purpose registry (WS-2 of the consolidation sprint) as a
first-class concept: a `PurposeDefinition` value object, a
`PurposeRegistry` service keyed by slug, and a declarative
`config/form_builder/purposes.php` registry with exactly the seven
purposes from ARCH-CONSOLIDATION §6.4.

Also rebuilds the morph-map in `AppServiceProvider::boot` into three
labelled blocks: (1) domain subject types derived from
`PurposeRegistry::allSubjectTypes()`, (2) non-purpose domain types
hardcoded with comments (form_schemas owner_types, activity-log
subjects), (3) framework types (spatie/activitylog; Sanctum stays
absent per addendum Q4).

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

api/config/form_builder/purposes.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Enums\FormBuilder\FormSubmissionMode;
+
+/*
+|--------------------------------------------------------------------------
+| Form Builder — Purpose registry (v1.0)
+|--------------------------------------------------------------------------
+|
+| Declarative set of purposes served by the universal form builder. v1.0
+| ships seven purposes. Adding a new purpose requires a code change (this
+| file) plus, typically, a new listener — per ARCH-CONSOLIDATION §3
+| besluit 4. Purposes are not user-defined.
+|
+| Each purpose declares:
+|   - label (NL): organizer-facing label
+|   - subject_type: morph alias used for form_submissions.subject_type
+|   - default_submission_mode: FormSubmissionMode enum case
+|   - allows_public_access: schema-level public submission without token
+|   - required_bindings: list of "{entity}.{attribute}" binding paths
+|                        that must be present on a schema before publish
+|
+*/
+
+return [
+
+    'event_registration' => [
+        'label' => 'Aanmelding vrijwilligers/crew',
+        'subject_type' => 'person',
+        'default_submission_mode' => FormSubmissionMode::SINGLE,
+        'allows_public_access' => true,
+        'required_bindings' => ['person.email', 'person.first_name', 'person.last_name'],
+    ],
+
+    'artist_advance' => [
+        'label' => 'Artiest advance',
+        'subject_type' => 'artist',
+        'default_submission_mode' => FormSubmissionMode::DRAFT_SINGLE,
+        'allows_public_access' => false,
+        'required_bindings' => [],
+    ],
+
+    'supplier_intake' => [
+        'label' => 'Leverancier intake',
+        'subject_type' => 'company',
+        'default_submission_mode' => FormSubmissionMode::SINGLE,
+        'allows_public_access' => false,
+        'required_bindings' => ['company.name'],
+    ],
+
+    'post_event_evaluation' => [
+        'label' => 'Evaluatie na afloop',
+        'subject_type' => 'person',
+        'default_submission_mode' => FormSubmissionMode::SINGLE,
+        'allows_public_access' => false,
+        'required_bindings' => [],
+    ],
+
+    'incident_report' => [
+        'label' => 'Incident-melding',
+        'subject_type' => 'person',
+        'default_submission_mode' => FormSubmissionMode::MULTIPLE,
+        'allows_public_access' => false,
+        'required_bindings' => [],
+    ],
+
+    'signature_contract' => [
+        'label' => 'Contract-ondertekening',
+        'subject_type' => 'user',
+        'default_submission_mode' => FormSubmissionMode::SINGLE,
+        'allows_public_access' => false,
+        'required_bindings' => [],
+    ],
+
+    'user_profile' => [
+        'label' => 'Profiel-update',
+        'subject_type' => 'user',
+        'default_submission_mode' => FormSubmissionMode::SINGLE,
+        'allows_public_access' => false,
+        'required_bindings' => [],
+    ],
+
+];