No passing OR lane changes in intersection. If something had happened and this ended up in court it would be 100% on the guy passing.
Doubtful. For 100% liability, the OP would have to prove that it was unreasonable to pass in that intersection even though there is no law specifically forbidding it and also that OP was not negligent in taking a left hand turn without signaling and checking to make sure the lane was clear for the turn. In a contributory negligence jurisdiction (and there are still a few states and DC in this category), any negligence on the part of OP would bar him from collecting from the passing bicyclist. Most states are comparative negligence, and it's probable that OP's award would be reduced by some percentage for the failure to signal and check.
I think there's a fundamental misconception here that passing a cyclist in an intersection is per se negligence or otherwise illegal (again, anyone want to actually produce a law forbidding it?). Judging by how many cars actually pass me in an intersection on any given ride where there's traffic, I really don't think that's a common view.