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/routes/_authenticated/lessons/enrollments/new.tsx

@@ -108,7 +108,7 @@ function NewEnrollmentPage() {
     },
     onSuccess: (enrollment) => {
       toast.success('Enrollment created')
-      navigate({ to: '/lessons/enrollments/$enrollmentId', params: { enrollmentId: enrollment.id }, search: {} as any })
+      navigate({ to: '/lessons/enrollments/$enrollmentId', params: { enrollmentId: enrollment.id }, search: {} as Record<string, unknown> })
     },
     onError: (err) => toast.error(err.message),
   })
@@ -141,7 +141,7 @@ function NewEnrollmentPage() {
   return (
     <div className="space-y-6 max-w-2xl">
       <div className="flex items-center gap-3">
-        <Button variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/enrollments', search: {} as any })}>
+        <Button variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/enrollments', search: {} as Record<string, unknown> })}>
           <ArrowLeft className="h-4 w-4" />
         </Button>
         <h1 className="text-2xl font-bold">New Enrollment</h1>
@@ -282,7 +282,7 @@ function NewEnrollmentPage() {
           <Button type="submit" disabled={mutation.isPending || !selectedMember || !selectedSlotId || !startDate} size="lg">
             {mutation.isPending ? 'Creating...' : 'Create Enrollment'}
           </Button>
-          <Button variant="secondary" type="button" size="lg" onClick={() => navigate({ to: '/lessons/enrollments', search: {} as any })}>
+          <Button variant="secondary" type="button" size="lg" onClick={() => navigate({ to: '/lessons/enrollments', search: {} as Record<string, unknown> })}>
             Cancel
           </Button>
         </div>