feat: registration section preferences with show_in_registration filtering and deduplication

Add show_in_registration and registration_description columns to festival_sections.
Registration form now shows deduplicated sections by name (across sub-events),
filtered by show_in_registration=true, grouped by category with card-based UI.
Section preferences use section_name instead of section_id.
Add GET/PUT registration-settings endpoints for festival-level bulk management.

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

api/database/migrations/2026_04_10_300000_add_registration_fields_to_festival_sections_table.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('festival_sections', function (Blueprint $table) {
+            $table->boolean('show_in_registration')->default(false)->after('timed_accreditations');
+            $table->text('registration_description')->nullable()->after('show_in_registration');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('festival_sections', function (Blueprint $table) {
+            $table->dropColumn(['show_in_registration', 'registration_description']);
+        });
+    }
+};