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/app/Http/Requests/Api/V1/StoreFestivalSectionRequest.php

@@ -31,6 +31,8 @@ final class StoreFestivalSectionRequest extends FormRequest
             'crew_accreditation_level' => ['nullable', 'string', 'max:50'],
             'public_form_accreditation_level' => ['nullable', 'string', 'max:50'],
             'timed_accreditations' => ['nullable', 'boolean'],
+            'show_in_registration' => ['nullable', 'boolean'],
+            'registration_description' => ['nullable', 'string', 'max:500'],
         ];
     }