feat: registration form fields, section preferences, tag sync & schema updates

Implement EAV system for dynamic event-specific registration fields
with organisation-level templates, person section preferences with
priority ranking, and TagSyncService for deferred tag_picker sync.

New tables: registration_field_templates, registration_form_fields,
person_field_values, person_section_preferences.
New columns: persons.remarks, events.registration_show_section_preferences,
events.registration_show_availability.

58 tests, 126 assertions — all 432 tests pass (zero regressions).

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

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

@@ -28,6 +28,8 @@ final class UpdateEventRequest extends FormRequest
             'event_type_label' => ['nullable', 'string', 'max:50'],
             'sub_event_label' => ['nullable', 'string', 'max:50'],
             'registration_welcome_text' => ['nullable', 'string', 'max:1000'],
+            'registration_show_section_preferences' => ['nullable', 'boolean'],
+            'registration_show_availability' => ['nullable', 'boolean'],
         ];
     }
 }