refactor company tests

[gabrielseco]

Note

Low Risk
Low risk: changes are limited to test fixtures and MSW handler setup, with no production logic modifications. Main risk is test brittleness if shared default handlers now return data that some tests implicitly relied on overriding.

Overview
Refactors onboarding-related tests to rely on shared MSW defaultHandlers instead of per-test stubs for GET /v1/companies/:companyId and benefit-offers endpoints.

Moves previously in-test fixtures (companyResponse, benefitOffersResponse, benefitOffersSchema) into common API fixtures by adding mockCompanyResponse in fixtures/companies.ts and introducing fixtures/employments.ts, and wires these into src/tests/handlers.ts. Updates invite/onboarding tests to reference mockCompanyResponse when overriding credit-risk scenarios, and removes redundant mocks/imports accordingly.

^{Written by Cursor Bugbot for commit 93f7093. This will update automatically on new commits. Configure here.}