Renames 'can register a new account and see check your email screen' to
'shows success message after registration' and asserts .bg-red-50 contains
'Account created! Please sign in.' instead of checking for a heading.
Updates 'can sign in with credentials' test to first register a fresh account
and assert the success message, then proceed with login.
Refs: CAR-822, PR cartsnitch/cartsnitch#181
Ports PR #181 intent from cartsnitch/cartsnitch to cartsnitch/app.
Removes registrationComplete, resendLoading, resendMessage state and the
handleResendVerification function. After successful signUp.email, now
sets setError('Account created! Please sign in.') instead of showing
the separate "Check your email" page.
Refs: CAR-822, CAR-818