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/database/seeders/DevSeeder.php

@@ -150,7 +150,11 @@ class DevSeeder extends Seeder
                 $this->personTags[$data['name']] = $tag;
             }
 
-            $this->command->info('  Organisation, 8 users, 6 companies, 7 crowd types, 10 person tags created');
+            // ── Registration Field Templates (system defaults) ──
+
+            \App\Services\RegistrationFieldTemplateService::seedSystemTemplates($this->org);
+
+            $this->command->info('  Organisation, 8 users, 6 companies, 7 crowd types, 10 person tags, 11 registration templates created');
         });
     }