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/UpdatePersonRequest.php

@@ -27,6 +27,7 @@ final class UpdatePersonRequest extends FormRequest
             'status' => ['sometimes', 'in:invited,applied,pending,approved,rejected,no_show'],
             'is_blacklisted' => ['sometimes', 'boolean'],
             'admin_notes' => ['nullable', 'string'],
+            'remarks' => ['nullable', 'string', 'max:5000'],
             'custom_fields' => ['nullable', 'array'],
         ];
     }