INSHASA, Congo — Congo’s election crisis deepened early Sunday when the Constitutional Court confirmed the win of Felix Tshisekedi, rejecting claims of fraud, and runner-up Martin Fayulu promptly declared himself the country’s “only legitimate president.” Fayulu’s supporters have alleged an extraordinary backroom deal by outgoing President Joseph Kabila to rig the vote in favor of the opposition after the ruling party’s candidate did so poorly that a Plan B was needed.