[whitezaddy]

Summary

Closes #1151

• Implemented split event notification banner (KeySplitBanner) on key detail and portfolio pages, displaying the split ratio, pre-split balance, and post-split balance for 48 hours after execution (Add key split event notification and updated balance display #1151).
• Added a "Split Applied" badge (SplitAppliedBadge) to highlight split keys in the portfolio positions table and profile holdings grid for 48 hours after a split event.
• Built keySplitEvents.service.ts and useKeySplit.ts to manage realtime SplitExecuted socket events, calculate balances accurately, auto-expire banners/badges after 48 hours, and immediately invalidate/refetch wallet holdings upon split execution.
• Added session dismissal support for the banner using sessionStorage so closing the banner clears it for the remainder of the session.
• Added unit and integration tests across utilities, components, hooks, and pages.

Testing

• pnpm lint (0 errors, 0 warnings)
• pnpm build (tsc -b && vite build succeeded)
• pnpm vitest run src/utils/__tests__/keySplit.utils.test.ts (22 passing tests)
• pnpm vitest run src/components/common/__tests__/SplitAppliedBadge.test.tsx (2 passing tests)
• pnpm vitest run src/components/common/__tests__/KeySplitBanner.test.tsx (4 passing tests)
• pnpm vitest run src/hooks/__tests__/useKeySplit.test.tsx (5 passing tests)
• pnpm vitest run src/pages/__tests__/CreatorDetailPage.keySplit.integration.test.tsx (4 passing tests)
• pnpm vitest run src/pages/__tests__/WalletPortfolioPage.keySplit.integration.test.tsx (3 passing tests)
• pnpm vitest run src/pages/__tests__/WalletPortfolioPage.test.tsx (6 passing tests)

Checklist

• Linked issue or backlog item (Add key split event notification and updated balance display #1151)
• Scope is limited to the stated change
• Updated docs if behavior or setup changed
• Added screenshots for UI changes when relevant