Build TopMoversCard component

[christabel888]

Context: Mirrors the frontend's TopAssetsCard extension (Stellar-Insightss/Stellar-inights#182), but mobile has no equivalent existing component -- this is new.

Where:

• New src/components/TopMoversCard.tsx

What to do:

• Build the card matching the pivot doc's example (asset, percent change, new-holder count).

Suggested approach:

1. Design around the pivot doc's example shape (asset, percent change, new-holder count) -- build the presentational component first with mock data, then wire Wire TopMoversCard to /api/v1/rankings/top-movers #43's real data in.

Watch out for:

• None beyond standard component hygiene -- this is genuinely new but well-scoped.

Definition of done:

• Component renders given mock/real data