refactor(client): remove orphaned dead logic flagged by ESLint (R2c)

- MobileBillRow: an autopayClass useMemo computed a badge class that was never
  rendered (dead since a refactor) -> removed.
- CategoriesPage: onRowKeyDown handler was never wired (keyboard toggle is now
  the dedicated chevron button, per the QA-B14-02 a11y fix) -> removed.
- BillModal: unused isDebtCategory derived flag -> removed.
Remaining lint warnings are unused imports / HMR / vestigial destructures
(non-correctness, non-blocking, now tracked by eslint).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/components/BillModal.jsx

@@ -142,7 +142,6 @@ export default function BillModal({ bill, initialBill, categories, onClose, onSa
   const [bulkUnmatch,        setBulkUnmatch]        = useState(null);
   const [bulkBusy,           setBulkBusy]           = useState(false);
 
-  const isDebtCategory = isDebtCat(categories, categoryId);
   const isSnowballCategory = isSnowballCat(categories, categoryId);
   const showOnSnowball = snowballInclude || (isSnowballCategory && !snowballExempt);
   const canAutoMarkPaid = autopay && autodraftStatus === 'assumed_paid';

client/components/MobileBillRow.jsx

@@ -21,13 +21,6 @@ export const MobileBillRow = React.memo(function MobileBillRow({ bill, onEdit, o
     );
   }, [bill.active]);
 
-  const autopayClass = useMemo(() => {
-    return cn(
-      'rounded bg-emerald-500/20 px-1.5 py-0.5 text-[10px] font-semibold text-emerald-300',
-      bill.autopay_enabled ? 'opacity-100' : 'opacity-0',
-    );
-  }, [bill.autopay_enabled]);
-
   const toggleBtnClass = useMemo(() => {
     return cn(
       'h-8 px-2.5 text-xs',

client/pages/CategoriesPage.jsx

@@ -270,13 +270,6 @@ export default function CategoriesPage() {
     });
   }
 
-  function onRowKeyDown(event, id) {
-    if (event.key === 'Enter' || event.key === ' ') {
-      event.preventDefault();
-      toggleCategory(id);
-    }
-  }
-
   async function handleAdd(e) {
     e.preventDefault();
     const trimmed = newName.trim();