phsl / new-api

Add comprehensive loading state support with skeleton animations for the SelectableButtonGroup component, improving user experience during data loading.

Key Changes:
- Add loading prop to SelectableButtonGroup with minimum 500ms display duration
- Implement skeleton buttons with proper Semi-UI Skeleton wrapper and active animation
- Use fixed skeleton count (6 items) to prevent visual jumping during load transitions
- Pass loading state through all pricing filter components hierarchy:
  - PricingSidebar and PricingFilterModal as container components
  - PricingDisplaySettings, PricingCategories, PricingGroups, PricingQuotaTypes as filter components

Technical Details:
- Reference CardTable.js implementation for consistent skeleton UI patterns
- Add useEffect hook for 500ms minimum loading duration control
- Support both checkbox and regular button skeleton modes
- Maintain responsive layout compatibility (mobile/desktop)
- Add proper JSDoc parameter documentation for loading prop

Fixes:
- Prevent skeleton count sudden changes that caused visual discontinuity
- Ensure proper skeleton animation with Semi-UI active parameter
- Maintain consistent loading experience across all filter components