feat(#2953): update Icon button component for V2

[twjeffery]

Summary

Updates the Icon Button component to integrate V2 design tokens, achieving V2 styling through token-driven architecture while maintaining full backwards compatibility with V1. This is a Token-Only update with minor code cleanup.

Changes

Token Integration

Updated Token References:

• Integrated new size-specific padding tokens (small-padding, medium-padding, large-padding)
• Added fallback chains for V1 compatibility
• Integrated focus state tokens that reference Input component for system-wide consistency

No New Props:

• Token-Only classification means no version prop needed
• V1 and V2 differentiated entirely through token packages

V2 Styling Updates

Spacing:

• Small buttons: 4px padding (unchanged)
• Medium buttons: 8px padding (increased from 4px for better clickability)
• Large buttons: 12px padding (increased from 8px for better hierarchy)

Colors:

• Light variant hover: Lighter grey background (greyscale.600 vs greyscale.700)
• Disabled states: Consistent greyscale.500 across all variants

Focus State:

• Focus tokens now reference Input component ({input.borderWidth.focus}, {input.color.border.focus})
• Maintains box-shadow focus treatment (border-based focus deferred to future update)
• System-wide consistency: changing Input focus automatically updates Icon Button

Related

• Parent issue: Design system 2.0 coded component update #2998
• Component issue: Icon Button 2.0 Update #2953
• Design tokens PR for Icon Button
• v2 Figma component