feat(frontend): contract list view

[Omoboi-dev]

Context
The first useful screen: which contracts are indexed and what their status is.

Task
Build a view that lists indexed contracts (id, first-seen ledger, status) using
the SDK.

Pointers

• Depends on the dashboard scaffold + an API endpoint listing contracts.
• Use @stardex/sdk.

Acceptance criteria

• Contracts render in a list/table
• Loading + empty states handled
• pnpm -r typecheck passes

Notes
🟢 Good first issue.