Add Vue components and API client for managing user custom attributes.
- Add userAttributes API client with CRUD operations
- Add UserAttributeForm component for displaying/editing attribute values
- Add UserAttributesConfigModal for attribute definition management
- Support all attribute types: text, textarea, number, email, url,
date, select, multi_select
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
