feat(client): polish winner demo celebration flow

[Vicsygold]

Close #841
PR doc:

Summary

Polished the winner announcement experience in the client app.

What changed

• Reworked the winner demo page into a full celebration screen.
• Added a confetti burst on mount with canvas-confetti.
• Added a typewriter-style wallet address reveal.
• Wired the winner banner to receive the winner announcement props and render the prize, value, and wallet summary.
• Added prefilled social share links for X and Telegram.
• Added Vitest coverage for the demo page and the banner snapshot.

Testing

• pnpm exec vitest --run src/components/RaffleWinnerBanner.spec.tsx src/pages/WinnerDemo.spec.tsx
• pnpm exec eslint src/components/RaffleWinnerBanner.tsx src/components/RaffleWinnerBanner.spec.tsx src/pages/WinnerDemo.tsx src/pages/WinnerDemo.spec.tsx

Notes

• pnpm install was run in client/, which refreshed pnpm-lock.yaml.

Commit message:

```text
feat(client): polish winner demo celebration flow

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