feat: registration section preferences with show_in_registration filtering and deduplication

Add show_in_registration and registration_description columns to festival_sections.
Registration form now shows deduplicated sections by name (across sub-events),
filtered by show_in_registration=true, grouped by category with card-based UI.
Section preferences use section_name instead of section_id.
Add GET/PUT registration-settings endpoints for festival-level bulk management.

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

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

@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+final class VolunteerRegistrationRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    protected function prepareForValidation(): void
+    {
+        $user = auth('sanctum')->user();
+
+        if ($user) {
+            $this->merge([
+                'name' => $user->name,
+                'email' => $user->email,
+                '_authenticated' => true,
+            ]);
+        }
+    }
+
+    /** @return array<string, mixed> */
+    public function rules(): array
+    {
+        return [
+            'name' => ['required_without:_authenticated', 'string', 'max:255'],
+            'email' => ['required_without:_authenticated', 'email', 'max:255'],
+            'phone' => ['nullable', 'string', 'max:50'],
+
+            'tshirt_size' => ['nullable', 'string', 'in:XS,S,M,L,XL,XXL,XXXL'],
+            'first_aid' => ['nullable', 'boolean'],
+            'allergies' => ['nullable', 'string', 'max:500'],
+            'access_requirements' => ['nullable', 'string', 'max:500'],
+            'driving_licence' => ['nullable', 'boolean'],
+
+            'motivation' => ['nullable', 'string', 'max:1000'],
+            'motivation_other' => ['nullable', 'string', 'max:500'],
+
+            'section_preferences' => ['nullable', 'array', 'max:5'],
+            'section_preferences.*.section_name' => ['required', 'string', 'max:255'],
+            'section_preferences.*.priority' => ['required', 'integer', 'min:1', 'max:5'],
+
+            'availabilities' => ['nullable', 'array'],
+            'availabilities.*.time_slot_id' => ['required', 'ulid', 'exists:time_slots,id'],
+            'availabilities.*.preference_level' => ['nullable', 'integer', 'min:1', 'max:5'],
+        ];
+    }
+}