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,

packages/admin/src/routes/_authenticated/lessons/enrollments/$enrollmentId.tsx

@@ -265,7 +265,7 @@ function DetailsTab({
                   onChange={(e) => setBillingInterval(e.target.value)}
                   className="w-20"
                 />
-                <Select value={billingUnit} onValueChange={setBillingUnit}>
+                <Select value={billingUnit} onValueChange={(v) => setBillingUnit(v as typeof billingUnit)}>
                   <SelectTrigger className="w-36"><SelectValue /></SelectTrigger>
                   <SelectContent>
                     {BILLING_UNITS.map((u) => (