refactor: optimize state initialization with lazy initializers

- Move billStates calculation into useState lazy initializer to prevent recalculation on re-renders
- Initialize allPaidMode based on billStates to reflect actual data state
- Use lazy initialization pattern for better performance
- Remove intermediate variables to simplify code

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

app/[locale]/home/multi-bill-edit/[year]/[month]/MultiBillEdit.tsx

@@ -26,18 +26,21 @@ export const MultiBillEdit: FC<MultiBillEditProps> = ({ locations, year, month }
     const t = useTranslations("multi-bill-edit");
     const router = useRouter();
 
-    // Initialize bill states from locations
+    const [isSaving, setIsSaving] = useState(false);
-    const initialBillStates: BillState[] = locations.flatMap(location =>
+
+    const [billStates, setBillStates] = useState<BillState[]>(() =>
+        locations.flatMap(location =>
             location.bills.map(bill => ({
                 locationId: location._id,
                 billId: bill._id,
                 paid: bill.paid,
             }))
+        )
     );
 
-    const [billStates, setBillStates] = useState<BillState[]>(initialBillStates);
+    const [allPaidMode, setAllPaidMode] = useState(() =>
-    const [isSaving, setIsSaving] = useState(false);
+        billStates.length > 0 && billStates.every(bill => bill.paid)
-    const [allPaidMode, setAllPaidMode] = useState(false);
+    );
 
     // Toggle individual bill paid status
     const handleBillToggle = (locationId: string, billId: string) => {