fix(e2e): abort mocked OAuth callbacks

[winetree94]

Summary

• abort the mocked OAuth callback navigation after capturing its authorization code
• wait for request failure before starting the next authorization flow
• eliminate the callback-versus-goto navigation race

Verification

• failing account-switch test repeated 10 times on Chromium and Firefox: 20 passed
• account-selection E2E on Chromium and Firefox: 14 passed
• pnpm verify:quick
• git diff --check