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/app/Http/Controllers/Api/V1/CheckEmailController.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Http\Controllers\Controller;
+use App\Http\Requests\Api\V1\CheckEmailRequest;
+use App\Models\User;
+use Illuminate\Http\JsonResponse;
+
+final class CheckEmailController extends Controller
+{
+    public function __invoke(CheckEmailRequest $request): JsonResponse
+    {
+        $exists = User::where('email', strtolower($request->validated('email')))->exists();
+
+        return response()->json(['exists' => $exists]);
+    }
+}

api/app/Http/Controllers/Api/V1/PersonController.php

@@ -9,17 +9,22 @@ use App\Http\Requests\Api\V1\StorePersonRequest;
 use App\Http\Requests\Api\V1\UpdatePersonRequest;
 use App\Http\Resources\Api\V1\PersonCollection;
 use App\Http\Resources\Api\V1\PersonResource;
+use App\Mail\RegistrationApprovedMail;
+use App\Mail\RegistrationRejectedMail;
 use App\Models\Event;
 use App\Models\Person;
 use App\Services\PersonIdentityService;
+use App\Services\TagSyncService;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use Illuminate\Support\Facades\Gate;
+use Illuminate\Support\Facades\Mail;
 
 final class PersonController extends Controller
 {
     public function __construct(
         private readonly PersonIdentityService $identityService,
+        private readonly TagSyncService $tagSyncService,
     ) {}
 
     public function index(Request $request, Event $event): PersonCollection
@@ -107,6 +112,27 @@ final class PersonController extends Controller
 
         $person->update(['status' => 'approved']);
 
+        $this->tagSyncService->syncFromRegistration($person);
+
+        if ($person->email) {
+            Mail::to($person->email)->queue(new RegistrationApprovedMail($person, $event));
+        }
+
+        return $this->success(new PersonResource($person->fresh()->load('crowdType')));
+    }
+
+    public function reject(Request $request, Event $event, Person $person): JsonResponse
+    {
+        Gate::authorize('approve', [$person, $event]);
+
+        $person->update(['status' => 'rejected']);
+
+        $reason = $request->input('reason');
+
+        if ($person->email) {
+            Mail::to($person->email)->queue(new RegistrationRejectedMail($person, $event, $reason));
+        }
+
         return $this->success(new PersonResource($person->fresh()->load('crowdType')));
     }
 }