Update U-matrix on rent changes

Ensure the U-matrix recalculates whenever rents are updated by clarifying dependencies and re-render behavior in RentDivisionPuzzle.tsx, so changes to individual rents trigger a recalculation of utilities (U = V - R) across all agents and rooms.

X-Lovable-Edit-ID: edt-a60b7332-4f67-4926-a402-d083626b1c12

src/components/RentDivisionPuzzle.tsx

@@ -46,11 +46,10 @@ const RentDivisionPuzzle = ({ onComplete }: RentDivisionPuzzleProps) => {
   const rentDiff = totalRent - currentTotal;
 
   // Compute U-matrix: utility[agent][room] = valuation - rent
-  const utilities = useMemo(() => {
-    return valuations.map((agentVals) =>
+  // Computed directly to ensure reactivity when rents change
+  const utilities = valuations.map((agentVals) =>
     agentVals.map((v, roomIdx) => v - rents[roomIdx])
   );
-  }, [valuations, rents]);
 
   // Find envy relationships
   const envyInfo = useMemo(() => {