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/app/Enums/FieldDisplayWidth.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Enums;
+
+enum FieldDisplayWidth: string
+{
+    case FULL = 'full';
+    case HALF = 'half';
+
+    public function label(): string
+    {
+        return match ($this) {
+            self::FULL => 'Volledige breedte',
+            self::HALF => 'Halve breedte',
+        };
+    }
+
+    /**
+     * Return the default display width for a given field type.
+     */
+    public static function defaultForFieldType(RegistrationFieldType $fieldType): self
+    {
+        return match ($fieldType) {
+            RegistrationFieldType::TEXT,
+            RegistrationFieldType::NUMBER,
+            RegistrationFieldType::SELECT,
+            RegistrationFieldType::BOOLEAN => self::HALF,
+
+            RegistrationFieldType::TEXTAREA,
+            RegistrationFieldType::RADIO,
+            RegistrationFieldType::CHECKBOX,
+            RegistrationFieldType::MULTISELECT,
+            RegistrationFieldType::TAG_PICKER => self::FULL,
+        };
+    }
+}