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/plans/$planId.tsx

@@ -93,7 +93,7 @@ function LessonPlanDetailPage() {
   return (
     <div className="space-y-6 max-w-3xl">
       <div className="flex items-center gap-3">
-        <Button variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/plans', search: {} as any })}>
+        <Button variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/plans', search: {} as Record<string, unknown> })}>
           <ArrowLeft className="h-4 w-4" />
         </Button>
         <div className="flex-1">

packages/admin/src/routes/_authenticated/lessons/plans/index.tsx

@@ -84,7 +84,7 @@ function LessonPlansPage() {
         order={params.order}
         onPageChange={setPage}
         onSort={setSort}
-        onRowClick={(p) => navigate({ to: '/lessons/plans/$planId', params: { planId: p.id }, search: {} as any })}
+        onRowClick={(p) => navigate({ to: '/lessons/plans/$planId', params: { planId: p.id }, search: {} as Record<string, unknown> })}
       />
     </div>
   )