feat(portal): multi-step volunteer registration form with public event endpoint

- Add GET /api/v1/public/events/{slug}/registration-data endpoint for fetching
  event sections and time slots without auth
- Create 5-step registration form: personal info, details, motivation, section
  preferences, availability
- VeeValidate + Zod validation per step with Dutch error messages
- Auth-aware: pre-fills name/email for authenticated users
- Mobile responsive with custom chip-based step indicator
- Success page with contextual actions (dashboard vs login)
- Types, composable (TanStack Query), and Zod schemas

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

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

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Http\Controllers\Controller;
+use App\Models\Event;
+use App\Models\FestivalSection;
+use App\Models\TimeSlot;
+use Illuminate\Http\JsonResponse;
+
+final class PublicRegistrationDataController extends Controller
+{
+    public function __invoke(string $slug): JsonResponse
+    {
+        $event = Event::where('slug', $slug)
+            ->where('status', 'registration_open')
+            ->first();
+
+        if ($event === null) {
+            abort(404, 'Event not found or not accepting registrations.');
+        }
+
+        $festivalEvent = $event->isSubEvent() ? $event->parent : $event;
+
+        $sectionQuery = FestivalSection::where('event_id', $festivalEvent->id)
+            ->where(function ($query) {
+                $query->where('type', '!=', 'cross_event')
+                    ->orWhereNull('type');
+            })
+            ->ordered();
+
+        if ($festivalEvent->isFestival()) {
+            $childIds = $festivalEvent->children()->pluck('id');
+            $sectionQuery->orWhere(function ($query) use ($childIds) {
+                $query->whereIn('event_id', $childIds)
+                    ->where(function ($q) {
+                        $q->where('type', '!=', 'cross_event')
+                            ->orWhereNull('type');
+                    });
+            });
+        }
+
+        $sections = $sectionQuery->get(['id', 'name', 'category', 'icon']);
+
+        $timeSlots = $festivalEvent->getAllRelevantTimeSlots()
+            ->where('person_type', 'VOLUNTEER')
+            ->values();
+
+        return response()->json([
+            'data' => [
+                'event' => [
+                    'id' => $festivalEvent->id,
+                    'name' => $festivalEvent->name,
+                    'start_date' => $festivalEvent->start_date->toDateString(),
+                    'end_date' => $festivalEvent->end_date->toDateString(),
+                    'organisation_id' => $festivalEvent->organisation_id,
+                ],
+                'sections' => $sections->map(fn (FestivalSection $section) => [
+                    'id' => $section->id,
+                    'name' => $section->name,
+                    'category' => $section->category,
+                    'icon' => $section->icon,
+                ]),
+                'time_slots' => $timeSlots->map(fn (TimeSlot $slot) => [
+                    'id' => $slot->id,
+                    'name' => $slot->name,
+                    'date' => $slot->date->toDateString(),
+                    'start_time' => $slot->start_time,
+                    'end_time' => $slot->end_time,
+                    'duration_hours' => $slot->duration_hours,
+                ]),
+            ],
+        ]);
+    }
+}