feat(account): add GET /account/:id/offers endpoint with pagination

[JoshuaEdd]

Closes #273

Summary

Adds GET /account/:id/offers endpoint to retrieve all open offers for a Stellar account on the DEX.

What changed

• src/routes/account.js — Rewrote /account/:id/offers handler:
  • Uses parsePaginationParams helper for limit, cursor, and order params
  • Normalises offer fields: offerId, selling, buying, price, amount, lastModifiedLedger
  • Returns data.offers array with total, limit, cursor metadata
  • Removed unused local validateLimit in favour of the shared one in validators.js
• types/index.d.ts — Added OfferAsset, OfferData, AccountOffersResponse types
• sdk/account.ts — Added typed getOffers() method with pagination options
• sdk/stellarkit-client.js — Added getAccountOffers() method
• tests/account.offers.test.js (new) — 7 mock-based tests covering success, empty, pagination, validation, and cursor
• tests/api.test.js — Updated 5 existing integration tests for new response shape (data.offers / offer.offerId), added cursor + order tests

Key design decisions

• Followed the existing paginated response pattern ({ offers, total, limit, cursor }) while renaming items → offers and id → offerId as required
• Reused parsePaginationParams from src/utils/pagination.js — already the standard pagination helper in the codebase
• Added .order(order) chain call to the Horizon query since the parsePaginationParams helper validates this param
• The local validateLimit duplicate was removed since it's no longer needed

Acceptance criteria checklist

• Returns success: true and data.offers array
• Supports limit and cursor query params
• Uses parsePaginationParams helper
• Normalised fields: offerId, selling, buying, price, amount, lastModifiedLedger
• Tests cover success, empty, pagination, invalid ID, invalid limit, and cursor paths

Test output

PASS tests/account.offers.test.js (7/7)
PASS tests/account.notFound.test.js (1/1)
PASS tests/api.test.js — offers tests (5/5)
Lint: 0 errors, 21 pre-existing warnings

All 13 offers-related tests pass. No regressions. Pre-existing test failures in api.test.js (cache warming, CORS, asset verify, fee-estimate/trends) are unrelated to this change.

Follow-ups

• The SDK could export the new OfferData type for external consumers
• A WebSocket stream endpoint for live offer updates could be a future enhancement

Security note

All user-supplied input (accountId, limit, order, cursor) is validated server-side before reaching Horizon. No sensitive data is exposed or logged.

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[Sulex45]

Kindly resolve conflicts