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/Policies/RegistrationFieldTemplatePolicy.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Policies;
+
+use App\Models\Organisation;
+use App\Models\RegistrationFieldTemplate;
+use App\Models\User;
+
+final class RegistrationFieldTemplatePolicy
+{
+    public function viewAny(User $user, Organisation $organisation): bool
+    {
+        return $user->hasRole('super_admin')
+            || $organisation->users()->where('user_id', $user->id)->exists();
+    }
+
+    public function create(User $user, Organisation $organisation): bool
+    {
+        return $this->canManageOrganisation($user, $organisation);
+    }
+
+    public function update(User $user, RegistrationFieldTemplate $template, Organisation $organisation): bool
+    {
+        if ($template->organisation_id !== $organisation->id) {
+            return false;
+        }
+
+        return $this->canManageOrganisation($user, $organisation);
+    }
+
+    public function delete(User $user, RegistrationFieldTemplate $template, Organisation $organisation): bool
+    {
+        if ($template->organisation_id !== $organisation->id) {
+            return false;
+        }
+
+        return $this->canManageOrganisation($user, $organisation);
+    }
+
+    private function canManageOrganisation(User $user, Organisation $organisation): bool
+    {
+        if ($user->hasRole('super_admin')) {
+            return true;
+        }
+
+        return $organisation->users()
+            ->where('user_id', $user->id)
+            ->wherePivot('role', 'org_admin')
+            ->exists();
+    }
+}