feat(form-builder): per-schema default_crowd_type_id replaces silent oldest() heuristic (WS-6)

Session 2's PersonProvisioner picked CrowdType::oldest() for the org —
silently wrong for multi-crowd_type orgs (Volunteer + Crew + Press are
three distinct crowd_types in one org). Schemas now declare their
target crowd_type explicitly via form_schemas.default_crowd_type_id.
RequiresDefaultCrowdType publish guard prevents misconfigured
event_registration schemas from publishing.

PersonProvisioner: oldest() fallback removed entirely. Misconfiguration
throws no_default_crowd_type at runtime; publish guard prevents it at
config time.

Migration uses a plain ulid() column without DB-level FK because
SQLite's table-rebuild on ALTER ADD FOREIGN KEY cascade-deletes
form_fields rows (form_fields.form_schema_id has cascadeOnDelete on
form_schemas). Application-level integrity via FormSchema::defaultCrowdType()
belongsTo + the publish guard + the runtime failsafe — three load-bearing
checks, none of which require the DB-level constraint.

Three pre-existing migration backfill tests bumped step counts +1 to
account for the new migration sitting between WS-5c and WS-5d:
FormFieldBindingMigrationTest (16→17, 14→15), FormFieldConfigBackfillAndDropTest
(11→12), FormFieldValidationRuleBackfillTest (14→15),
ConditionalLogicBackfillTest (5→6).

Six event_registration test fixtures updated to set default_crowd_type_id
to satisfy the new publish guard.

FormBuilderDevSeeder.resolveDefaultCrowdTypeId() — VOLUNTEER → first-active
→ create-as-needed fallback chain; documented contract for future seeders.

SCHEMA.md updated to v2.7.
Refs: RFC-WS-6.md v1.1 §3 Q8 addendum (Task 4 of this session)

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

api/tests/Unit/FormBuilder/Bindings/PersonProvisionerTest.php

@@ -123,6 +123,26 @@ final class PersonProvisionerTest extends TestCase
         });
     }
 
+    public function test_throws_when_schema_has_no_default_crowd_type(): void
+    {
+        $submission = $this->makeSubmissionWithEmail('jan@example.nl');
+        // Clear the field that the helper set up to satisfy the new contract.
+        /** @var FormSchema $schema */
+        $schema = $submission->schema;
+        $schema->default_crowd_type_id = null;
+        $schema->save();
+        $submission = $submission->fresh(['schema']);
+
+        DB::transaction(function () use ($submission): void {
+            try {
+                $this->provisioner()->provisionFromSubmission($submission);
+                $this->fail('Expected PersonProvisioningException');
+            } catch (PersonProvisioningException $e) {
+                $this->assertSame('no_default_crowd_type', $e->reasonCode);
+            }
+        });
+    }
+
     public function test_throws_when_identity_key_form_value_absent(): void
     {
         // Schema has the binding, but no form_value row was written
@@ -162,8 +182,12 @@ final class PersonProvisionerTest extends TestCase
 
         // PersonProvisioner needs an active CrowdType in the org to set
         // crowd_type_id on a freshly-provisioned Person (NOT NULL column).
-        if (! CrowdType::query()->where('organisation_id', $organisation->id)->where('is_active', true)->exists()) {
-            CrowdType::factory()->create([
+        $crowdType = CrowdType::query()
+            ->where('organisation_id', $organisation->id)
+            ->where('is_active', true)
+            ->first();
+        if ($crowdType === null) {
+            $crowdType = CrowdType::factory()->create([
                 'organisation_id' => $organisation->id,
                 'is_active' => true,
             ]);
@@ -171,6 +195,7 @@ final class PersonProvisionerTest extends TestCase
 
         $schema = FormSchema::factory()->create([
             'organisation_id' => $organisation->id,
+            'default_crowd_type_id' => $crowdType->id,
         ]);
 
         $emailField = FormField::factory()->create([

api/tests/Unit/FormBuilder/Publishing/RequiresDefaultCrowdTypeTest.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Unit\FormBuilder\Publishing;
+
+use App\FormBuilder\Publishing\RequiresDefaultCrowdType;
+use App\Models\CrowdType;
+use App\Models\FormBuilder\FormSchema;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+final class RequiresDefaultCrowdTypeTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_passes_when_default_crowd_type_id_set(): void
+    {
+        $schema = FormSchema::factory()->create();
+        $crowdType = CrowdType::factory()->create([
+            'organisation_id' => $schema->organisation_id,
+        ]);
+        $schema->default_crowd_type_id = $crowdType->id;
+        $schema->save();
+
+        $result = (new RequiresDefaultCrowdType())->evaluate($schema->fresh());
+        $this->assertTrue($result->passed);
+        $this->assertSame('requires_default_crowd_type', $result->guardCode);
+    }
+
+    public function test_fails_when_default_crowd_type_id_null(): void
+    {
+        $schema = FormSchema::factory()->create();
+        $this->assertNull($schema->default_crowd_type_id);
+
+        $result = (new RequiresDefaultCrowdType())->evaluate($schema);
+        $this->assertFalse($result->passed);
+        $this->assertSame('requires_default_crowd_type', $result->guardCode);
+        $this->assertSame(
+            'form_builder_publish_guards.requires_default_crowd_type',
+            $result->messageKey,
+        );
+    }
+}