test(api): add integration tests for transfer route handlers

[0xDeon]

Summary

Closes #29

• Adds Jest + ts-jest + supertest as dev dependencies; wires up npm test script and jest config in package.json
• Adds "types": ["node", "jest"] to tsconfig.json so Jest globals resolve correctly in the IDE
• Creates src/__tests__/routes/transfers.test.ts with 36 integration tests covering all transfer route handlers via HTTP (supertest), with all DB and RPC calls mocked

What was implemented

All 5 route handlers are tested:

Route	Tests
GET /transfers/incoming/:address	Base fetch, contractId, fromDate/toDate, invalid dates → 400, eventType (valid, multi, invalid → 400), limit/offset, fromLedger/toLedger, unknown address → empty, displayAmount
GET /transfers/outgoing/:address	Base fetch, direction wired to outgoing, displayAmount large i128, invalid eventType → 400
GET /transfers/address/:address	Combined transfers with direction field, pagination, contractId, invalid toDate → 400
GET /transfers/tx/:txHash	Multi-transfer tx, unknown txHash → empty, exact hash forwarded
GET /summary/:address	Token aggregates with display fields, invalid date → 400, unknown address → empty, date window forwarded

Seed data: 20 transfers covering incoming/outgoing, mint/burn/clawback/transfer event types, two token contracts, two addresses, varied timestamps and ledger numbers.

Edge cases for toDisplayAmount: 0 stroops, 1 stroop, 1 token (10 000 000), large i128 value.

How it was tested

npm test
# → Test Suites: 1 passed, 1 total
# → Tests:       36 passed, 36 total

All 36 tests pass with zero TS errors.

Manual test steps

git checkout test/transfer-route-handlers
npm install
npm test

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