[FR]: Add legacy-pattern callout in COMPONENT_CREATION_GUIDE.md

Describe the problem

The guide documents the object-with-variant-methods pattern as the standard. Many existing components (Tags, Buttons) use per-variant top-level functions. Contributors studying existing code see a pattern the guide does not describe.

Describe the solution

Add a note near the architecture section stating that existing components may use a legacy pattern (per-variant top-level functions) and that new components should follow the object pattern.

Additional context

Priority: Medium. Effort: XS.