feat: add MSW for integration test mocking

Install Mock Service Worker (MSW) and configure it for vitest.
Write one integration test for usePurchases hook using MSW.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/test/mocks/server.ts

@@ -0,0 +1,4 @@
+import { setupServer } from 'msw/node'
+import { handlers } from './handlers'
+
+export const server = setupServer(...handlers)