feat(api): extend registration endpoints with dynamic fields and section preferences

- PublicRegistrationData now returns registration_fields (portal-visible only),
  form toggles, and available_tags for tag_picker fields
- Volunteer registration accepts field_values and section_preferences with
  festival_section_id, processed via existing services
- PortalMe eager-loads fieldValues and sectionPreferences
- Section preferences now use the proper relational table instead of custom_fields JSON

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

api/app/Services/VolunteerRegistrationService.php

@@ -19,6 +19,8 @@ final class VolunteerRegistrationService
 {
     public function __construct(
         private readonly PersonIdentityService $identityService,
+        private readonly RegistrationFormFieldService $registrationFormFieldService,
+        private readonly PersonSectionPreferenceService $personSectionPreferenceService,
     ) {}
 
     /**
@@ -62,17 +64,26 @@ final class VolunteerRegistrationService
                         'driving_licence' => $validated['driving_licence'] ?? false,
                         'motivation' => $validated['motivation'] ?? null,
                         'motivation_other' => $validated['motivation_other'] ?? null,
-                        'section_preferences' => collect($validated['section_preferences'] ?? [])
-                            ->map(fn ($pref) => [
-                                'section_name' => $pref['section_name'],
-                                'priority' => $pref['priority'],
-                            ])->toArray(),
                     ],
                 ]
             );
 
             $this->syncAvailabilities($person, $festivalEvent, $validated['availabilities'] ?? []);
 
+            if (!empty($validated['field_values'])) {
+                $this->registrationFormFieldService->upsertPersonValues(
+                    $person,
+                    $validated['field_values']
+                );
+            }
+
+            if (!empty($validated['section_preferences'])) {
+                $this->personSectionPreferenceService->replacePreferences(
+                    $person,
+                    $validated['section_preferences']
+                );
+            }
+
             if ($user === null) {
                 $this->detectIdentityMatch($person);
             }