[Event] Prevent `contract_signed` validation from blocking updates by admins

[garyhtou]

Please see https://hackclub.slack.com/archives/C026RKHLPNJ/p1758917526179979

hcb/app/models/event.rb

Lines 907 to 912 in ca3cece

	def contract_signed
	return if organizer_position_contracts.signed.any? || organizer_position_contracts.none? || !plan.contract_required? || Rails.env.development?
	errors.add(:base, "Missing a contract signee, non-demo mode organizations must have a contract signee.")
	end

either allow admins to bypass this. or allow admins to bypass this for specific fields.

[garyhtou]

@leowilkin, @sampoder had added #11767, which I think largely handles this issue.

Leo or anyone else, do you know if anyone has experienced this issue in the past 3 weeks (since that PR was merged)? I'm going to close this ticket for the time being, but we can reopen if needed!