Surface builder presets for button/card components once they ship

[jackgranatowski]

Idea

When the framework's .sf-btn / .sf-card components land, expose their variants as ready-to-apply presets in the Bricks and Gutenberg integrations (class insertion + live preview), so users get one-click buttons/cards instead of hand-adding classes.

Why

Buttons and cards are the two most-used building blocks on typical business/marketing pages. The plugin already has class-hint/inventory plumbing; this is UI wiring on top once the components are live.

Scope / notes

• Depends on the framework shipping .sf-btn/.sf-card (tracked framework-side).
• Reuse existing class-hints data; add preset entries + preview.

Acceptance

• Button/card variant presets selectable in Bricks + Gutenberg with live preview