test(web): cover checkout return url handling

[cyncui]

why

closes #326.

checkout return banners need to survive strict mode while the url loses only the consumed billing parameter. these component tests protect that behavior, including a fresh mount at the cleaned url.

scope

• cover success and cancellation banners with repeated query keys and a fragment.
• cover absent and unknown outcomes without url changes.

blast radius

only web component tests change. the tests use mocked organisation data and make no payment request.

verification

• npm test: 71 passed.
• npm run typecheck: passed with a temporary declaration for the unavailable generated wasm bindings; the declaration was removed.
• chrome: the actual panel displayed each recognized banner once, preserved unrelated url parts, and left absent or unknown outcomes unchanged. api and vault imports were stubbed.
• git diff --check: passed.