“Unlike the FLA, which presumes that couples are entitled to an equal share of net family property accumulated during marriage, there is no presumption that a finding of unjust enrichment entitles a claimant to a half interest in the property. The extent of the claimant’s interest must be proportionate to their contributions: Kerr, at para. 102. When the contributions are unequal, the shares should be unequal: Kerr, at paras. 84-85.”