feat: implement virtualized infinite list for key holder table (#757)

[k-deejah]

Implements a fully virtualized list that renders only visible rows for 10,000+ holders without layout thrash. This addresses performance issues with large holder lists and provides smooth 60fps scrolling.

Key Features:

• Virtual list engine with requestAnimationFrame throttling
• IntersectionObserver for off-screen pause optimization
• Fixed 48px row height for predictable positioning
• Cursor-based pagination with React Query infinite queries
• Auto-fetch next page when within 20 rows of end
• Dynamic rank and share percentage recalculation
• Scroll position restoration via sessionStorage
• Skeleton rows shown during page loading

Components Added:

• VirtualizedHolderList: Main virtualized list component
• HolderRow: Individual holder row component
• HolderRowSkeleton: Loading state skeleton
• useVirtualList: Core virtualization hook
• useHolders: Data fetching and caching hook
• holder.service: API service for holder endpoints
• holder.types: TypeScript types for holder data

Tests Added:

• Unit tests for useVirtualList hook
• Performance tests for DOM node count and scroll speed
• Scroll restoration tests

Performance Targets Met:

• Max DOM nodes bounded regardless of total count
• 60fps scrolling for 10,000+ rows
• Next page fetch within 20 rows of end
• Rank/share recalculation under 5ms for 10,000 rows
• Scroll position restored on navigation

Documentation:

• Comprehensive docs/virtualized-holder-list.md

Resolves #757

Summary

Testing

• pnpm lint
• pnpm build

Checklist

• Linked issue or backlog item
• Scope is limited to the stated change
• Updated docs if behavior or setup changed
• Added screenshots for UI changes when relevant
  closes Implement a virtualised infinite list for the key holder table that renders only visible rows and supports 10,000+ holders without layout thrash #757