feat(api): registration auth, account creation, check-email & email notifications

- Add POST /public/check-email endpoint with rate limiting (10/min)
- Create user accounts during volunteer registration (new or returning)
- Returning volunteers authenticate with existing password
- Add password validation to VolunteerRegistrationRequest
- Normalize emails to lowercase throughout registration flow
- Handle race condition on duplicate accounts gracefully
- Create RegistrationConfirmationMail, RegistrationApprovedMail, RegistrationRejectedMail
- Wire approval/rejection emails into PersonController
- Add POST persons/{person}/reject endpoint
- Trigger TagSyncService on registration and approval
- Add CheckEmailTest, PersonApprovalEmailTest, extend VolunteerRegistrationTest

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/tests/Feature/Api/V1/RegistrationSettingsTest.php

@@ -195,8 +195,10 @@ class RegistrationSettingsTest extends TestCase
             ->assertJsonPath('data.0.section_count', 1);
     }
 
-    public function test_section_preferences_stored_as_section_name(): void
+    public function test_section_preferences_stored_in_table(): void
     {
+        \Illuminate\Support\Facades\Mail::fake();
+
         // This is a regression check for the VolunteerRegistration flow
         $event = Event::factory()->create([
             'organisation_id' => $this->organisation->id,
@@ -207,7 +209,7 @@ class RegistrationSettingsTest extends TestCase
             'organisation_id' => $this->organisation->id,
         ]);
 
-        FestivalSection::factory()->create([
+        $section = FestivalSection::factory()->create([
             'event_id' => $event->id,
             'name' => 'Backstage',
             'show_in_registration' => true,
@@ -217,18 +219,20 @@ class RegistrationSettingsTest extends TestCase
             'first_name' => 'Test',
             'last_name' => 'Vrijwilliger',
             'email' => 'test-section-pref@example.nl',
+            'password' => 'wachtwoord123',
             'section_preferences' => [
-                ['section_name' => 'Backstage', 'priority' => 1],
+                ['festival_section_id' => $section->id, 'priority' => 1],
             ],
         ]);
 
         $response->assertStatus(201);
 
         $person = \App\Models\Person::where('email', 'test-section-pref@example.nl')->first();
-        $prefs = $person->custom_fields['section_preferences'];
 
-        $this->assertCount(1, $prefs);
-        $this->assertEquals('Backstage', $prefs[0]['section_name']);
-        $this->assertEquals(1, $prefs[0]['priority']);
+        $this->assertDatabaseHas('person_section_preferences', [
+            'person_id' => $person->id,
+            'festival_section_id' => $section->id,
+            'priority' => 1,
+        ]);
     }
 }