feat(sdk): implement pagination cursors for getGigs()

[stephanieoghenemega-eng]

Closes #24

Summary

Adds getGigs() to TrustFlowEscrowClient with cursor-based pagination matching the backend schema. Each response carries a nextCursor to pass on the next call; null means the last page has been reached.

Changes

src/types/contract.ts

Added optional apiBaseUrl and apiKey to ContractConfig so the escrow client can reach the backend REST API:

export interface ContractConfig {
  contractId: string;
  network: 'TESTNET' | 'MAINNET';
  rpcUrl: string;
  networkPassphrase: string;
  apiBaseUrl?: string;
  apiKey?: string;
}

src/types/index.ts

Two new exported types:

export interface GetGigsParams {
  cursor?: string;       // omit to start from the first page
  limit?: number;        // default 20, capped at 100
  status?: EscrowState['status'];
  depositor?: StellarAddress;
  beneficiary?: StellarAddress;
}

export interface GigsPage {
  data: EscrowState[];
  nextCursor: string | null;
  hasMore: boolean;
}

src/escrow/client.ts

New getGigs(params?) on TrustFlowEscrowClient:

• Returns { ok: false, error: 'apiBaseUrl is required...' } when unconfigured
• Caps limit at 100 client-side before the request is sent
• Sends Authorization: Bearer <apiKey> when apiKey is present
• Wraps network failures in { ok: false, error: 'Network error: ...' } — consistent with SDKResult<T> across the codebase

Paginate all results:

let cursor: string | undefined;
do {
  const result = await client.getGigs({ cursor, limit: 20, status: 'active' });
  if (!result.ok) { console.error(result.error); break; }
  processBatch(result.data.data);
  cursor = result.data.nextCursor ?? undefined;
} while (cursor);

tests/gigs.test.ts

7 Jest tests covering:

• Missing apiBaseUrl → { ok: false }
• Empty first page response
• All 5 query params forwarded correctly (cursor, limit, status, depositor, beneficiary)
• limit: 500 capped to limit=100 in the URL
• Authorization header present when apiKey is set
• Multi-page cursor traversal chaining nextCursor across two pages
• Non-2xx and network error paths

Test plan

npm test -- gigs
npm run build