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/Http/Resources/Api/V1/RegistrationFormFieldResource.php

@@ -20,6 +20,7 @@ final class RegistrationFormFieldResource extends JsonResource
             'slug' => $this->slug,
             'field_type' => $this->field_type->value,
             'options' => $this->options,
+            'normalized_options' => $this->normalized_options,
             'tag_category' => $this->tag_category,
             'is_required' => $this->is_required,
             'is_portal_visible' => $this->is_portal_visible,
@@ -28,6 +29,7 @@ final class RegistrationFormFieldResource extends JsonResource
             'section' => $this->section,
             'help_text' => $this->help_text,
             'sort_order' => $this->sort_order,
+            'display_width' => $this->display_width->value,
             'created_at' => $this->created_at->toIso8601String(),
             'updated_at' => $this->updated_at->toIso8601String(),
             'available_tags' => $this->when(