fix: resolve all frontend lint errors and warnings

Replace all `any` types with proper types across 36 files:
- TanStack Router search params: `{} as Record<string, unknown>`
- API response pagination: proper typed interface
- DataTable column casts: remove unnecessary `as any`
- Function params and event handlers: use specific types
- Remove unused imports and variables in POS components

Frontend lint now passes with 0 errors and 0 warnings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/components/pos/pos-item-panel.tsx

@@ -14,7 +14,7 @@ interface POSItemPanelProps {
   transaction: Transaction | null
 }
 
-export function POSItemPanel({ transaction }: POSItemPanelProps) {
+export function POSItemPanel({ transaction: _transaction }: POSItemPanelProps) {
   const queryClient = useQueryClient()
   const { currentTransactionId, setTransaction, locationId } = usePOSStore()
   const [search, setSearch] = useState('')