feat(hooks): add useSettlementBreakdown hook for post-delivery fund distribution

[BigManly4]

Closes #782

Summary

Adds useSettlementBreakdown, which fetches the finalized settlement for an escrow from GET /api/escrow/{id}/settlement and polls until the release transaction reaches a terminal state.

Changes

• services/escrowSettlementService.ts: calls the settlement endpoint through the shared apiClient, maps axios failures to a SettlementServiceError (backend message, 404 message, or generic fallback) and exposes isTerminalStatus.
• hooks/useSettlementBreakdown.ts: TanStack Query hook. It returns settlement, formatted amounts, taxBreakdown, explorerUrl, isLoading, isFetching, isFinalizing, isTerminal, error and refetch.
  • Polls every 5s (configurable) while the status is pending or finalizing, and stops on confirmed or failed.
  • Does not retry 4xx errors. Retries 5xx and network errors twice.
• types/settlementBreakdown.ts: SettlementBreakdown with driver payout, platform fee and rate, tax withholdings, held amount and reason, remaining balance, transaction hash and ledger, and delivery summary.
• lib/settlementFormatters.ts: asset amount formatting (Stellar 7-decimal precision), percentage formatting and the stellar.expert transaction URL builder.

Layering: Component -> useSettlementBreakdown -> escrowSettlementService -> backend. Test data lives in hooks/__tests__/fixtures/settlementApiResponses.ts. Nothing is mocked inline in the source.

Tests

• hooks/__tests__/useSettlementBreakdown.test.tsx (11): structured data, formatted values, tax breakdown, explorer link, polling until confirmed or failed, no retry on 4xx, retry on 5xx, recovery through refetch, disabled or missing id.
• services/__tests__/escrowSettlementService.test.ts (10) and lib/__tests__/settlementFormatters.test.ts (4).
• 25 passing. The hook has 100% coverage.

Note: CI on main is already failing at the Lint step because of existing errors (for example the parse error in app/error.tsx). The files in this PR pass eslint and tsc --noEmit with no errors.

Screenshots

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[johdanike]

Conflicts!!
I'd fix anyways