fix: suppress navigate search type error in usePagination; fix setBillingUnit cast

- use-pagination.ts: ts-expect-error on navigate call — search type resolves as never without route context, safe with strict:false
- $enrollmentId.tsx: wrap onValueChange to cast string to billingUnit union type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/admin/src/hooks/use-pagination.ts

@@ -22,6 +22,7 @@ export function usePagination() {
   }
 
   function setParams(updates: Partial<PaginationSearch>) {
+    // @ts-expect-error: navigate without a route context resolves search as never; safe here since we use strict:false
     navigate({
       search: (prev: any) => ({
         ...prev,