Use UmbTextStyles instead of UUITextStyles in news card component

[Copilot]

Addresses review feedback to align with codebase conventions for text styling.

Changes

• Import: Changed from UUITextStyles (external UUI library) to UmbTextStyles (backoffice wrapper)
• Path: '@umbraco-cms/backoffice/external/uui' → '@umbraco-cms/backoffice/style'

Rationale

UmbTextStyles wraps UUITextStyles and adds anchor tag styling:

export const UmbTextStyles = css`
  ${UUITextStyles}
  
  a {
    color: var(--uui-color-interactive);
  }
  a:hover, a:focus {
    color: var(--uui-color-interactive-emphasis);
  }
`;

This pattern is used consistently across 20+ components in the codebase.

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