Add component and end-to-end tests for the core payment flow

[collinsadi]

The 18 Vitest suites cover crypto, lifecycle, and policy logic, but there are no component or end-to-end tests, so UI regressions in the register, receive, and claim path are not caught. We should add jsdom component tests for SendView recipient and amount validation, ReceiveView copy, and AddressDisplay, plus one integration test of the register, receive-via-link, and claim flow with mocked contract calls.

Acceptance criteria

• Component tests exist for the three views above.
• One green integration test exercises the payment lifecycle.