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/routes/api.php

@@ -2,6 +2,7 @@
 
 declare(strict_types=1);
 
+use App\Http\Controllers\Api\V1\CheckEmailController;
 use App\Http\Controllers\Api\V1\CompanyController;
 use App\Http\Controllers\Api\V1\CrowdListController;
 use App\Http\Controllers\Api\V1\CrowdTypeController;
@@ -60,6 +61,7 @@ Route::post('invitations/{token}/accept', [InvitationController::class, 'accept'
 
 // Public portal routes
 Route::get('public/events/{slug}/registration-data', PublicRegistrationDataController::class);
+Route::post('public/check-email', CheckEmailController::class)->middleware('throttle:10,1');
 Route::post('events/{event}/volunteer-register', VolunteerRegistrationController::class);
 Route::post('portal/token-auth', [PortalTokenController::class, 'auth']);
 
@@ -164,6 +166,7 @@ Route::middleware('auth:sanctum')->group(function () {
 
         Route::apiResource('persons', PersonController::class);
         Route::post('persons/{person}/approve', [PersonController::class, 'approve']);
+        Route::post('persons/{person}/reject', [PersonController::class, 'reject']);
 
         // Volunteer availabilities
         Route::get('persons/{person}/availabilities', [VolunteerAvailabilityController::class, 'index']);