[FR]: Update incomplete Button variant list in COMPONENT_CREATION_GUIDE.md

Describe the problem

The guide lists "Filled, Outlined, Ghost, Tinted, Contrast" but ButtonStyle.kt also contains Underline, and additional variant files exist (Boost, Danger, Success, Primary, Secondary, Tertiary, Ai, Text, Underlined).

Describe the solution

Update the variant list to match reality, or use a simpler reference component.

Additional context

Priority: Low. Effort: XS.