feat: replace mock data with live API calls

[collinsezedike]

Closes #35

Summary

• Wires VaultList and PortfolioSummary to live API via TanStack Query hooks (useVaults, usePositions)
• Adds GET /api/v1/positions/:publicKey stub route to the Fastify API
• Wraps the app in QueryClientProvider; deletes mockData.ts entirely
• Adds Vite dev proxy (/api → localhost:3001) to eliminate CORS in development
• Declares "type": "module" across API and shared packages to fix ESM top-level await errors
• Replaces bare <p> empty states with a reusable EmptyState component (icon + title + description)

Test plan

• pnpm dev starts both API and web without errors
• GET /api/v1/vaults returns { vaults: [] } through the proxy
• Vault list renders the empty state card (not a plain text string)
• Connecting a wallet shows the portfolio empty state
• Loading skeletons appear before data resolves
• pnpm lint && pnpm typecheck && pnpm test all pass

[collinsezedike]

Good progress. Mock data is fully gone. TanStack Query is wired correctly. The Vite proxy is a clean dev solution, and the empty states and skeletons are solid.

The only thing that needs fixing before this merges is the publicKey! assertion in usePositions which should be an explicit null guard instead. The unmatched position row rendering is also worth cleaning up. Raw vault IDs shouldn't reach the UI.

Everything else is nits.