feat: event registration branding with vertical wizard layout

- Add registration_banner_url, registration_welcome_text, registration_logo_url
  columns to events table with migration
- Add uploadImage endpoint (POST .../upload-image) with form request validation
  for banner and logo images (jpg/png/webp, max 5MB)
- Include branding fields in EventResource and PublicRegistrationDataController
- Build registration settings UI in organizer event settings page with
  banner/logo upload and welcome text editor
- Redesign portal registration page: hero banner with gradient overlay,
  welcome text card, vertical step navigation (desktop) / horizontal chips
  (mobile), two-column form fields with density="comfortable"
- Update success page with event banner and consistent branding
- Seed welcome text for Echt Feesten 2026
- Add 9 PHPUnit tests covering image upload, branding fields in API responses

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

api/app/Http/Requests/Api/V1/UpdateEventRequest.php

@@ -27,6 +27,7 @@ final class UpdateEventRequest extends FormRequest
             'event_type' => ['sometimes', 'in:event,festival,series'],
             'event_type_label' => ['nullable', 'string', 'max:50'],
             'sub_event_label' => ['nullable', 'string', 'max:50'],
+            'registration_welcome_text' => ['nullable', 'string', 'max:1000'],
         ];
     }
 }

api/app/Http/Requests/Api/V1/UploadEventImageRequest.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+final class UploadEventImageRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /** @return array<string, mixed> */
+    public function rules(): array
+    {
+        return [
+            'image' => ['required', 'image', 'mimes:jpg,jpeg,png,webp', 'max:5120'],
+            'type' => ['required', 'in:banner,logo'],
+        ];
+    }
+}