feat: registration form field display_width and option descriptions

Add configurable column widths (full/half) and optional descriptions
for radio/select/checkbox options on registration form fields.

- Migration adds display_width column to both tables
- FieldDisplayWidth enum with smart defaults per field type
- normalized_options accessor for backwards-compatible option format
- Portal form renderer uses display_width for VRow/VCol grid layout
- Radio/select/checkbox options render with descriptions
- Admin field editor supports display_width toggle and description input
- System templates updated with appropriate widths and descriptions

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

api/database/factories/RegistrationFieldTemplateFactory.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Database\Factories;
 
+use App\Enums\FieldDisplayWidth;
 use App\Enums\RegistrationFieldType;
 use App\Models\Organisation;
 use App\Models\RegistrationFieldTemplate;
@@ -34,6 +35,7 @@ final class RegistrationFieldTemplateFactory extends Factory
             'section' => null,
             'help_text' => null,
             'sort_order' => fake()->numberBetween(0, 20),
+            'display_width' => FieldDisplayWidth::FULL,
             'is_system' => false,
             'is_active' => true,
         ];
@@ -57,6 +59,7 @@ final class RegistrationFieldTemplateFactory extends Factory
             'field_type' => RegistrationFieldType::SELECT,
             'options' => ['XS', 'S', 'M', 'L', 'XL', 'XXL', 'XXXL'],
             'is_filterable' => true,
+            'display_width' => FieldDisplayWidth::HALF,
         ]);
     }
 
@@ -67,6 +70,7 @@ final class RegistrationFieldTemplateFactory extends Factory
             'slug' => 'ehbo-bhv-diploma',
             'field_type' => RegistrationFieldType::BOOLEAN,
             'is_filterable' => true,
+            'display_width' => FieldDisplayWidth::HALF,
         ]);
     }
 
@@ -77,6 +81,7 @@ final class RegistrationFieldTemplateFactory extends Factory
             'slug' => 'certificaten-vaardigheden',
             'field_type' => RegistrationFieldType::TAG_PICKER,
             'is_filterable' => true,
+            'display_width' => FieldDisplayWidth::FULL,
         ]);
     }
 }