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/templates/new.tsx

@@ -45,7 +45,7 @@ function NewTemplatePage() {
       }),
     onSuccess: (template) => {
       toast.success('Template created')
-      navigate({ to: '/lessons/templates/$templateId', params: { templateId: template.id }, search: {} as any })
+      navigate({ to: '/lessons/templates/$templateId', params: { templateId: template.id }, search: {} as Record<string, unknown> })
     },
     onError: (err) => toast.error(err.message),
   })
@@ -63,7 +63,7 @@ function NewTemplatePage() {
   return (
     <form onSubmit={handleSubmit} className="space-y-6 max-w-3xl">
       <div className="flex items-center gap-3">
-        <Button type="button" variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/templates', search: {} as any })}>
+        <Button type="button" variant="ghost" size="sm" onClick={() => navigate({ to: '/lessons/templates', search: {} as Record<string, unknown> })}>
           <ArrowLeft className="h-4 w-4" />
         </Button>
         <h1 className="text-2xl font-bold">New Template</h1>
@@ -112,7 +112,7 @@ function NewTemplatePage() {
         <Button type="submit" disabled={mutation.isPending || !name.trim() || !allSectionsValid} size="lg">
           {mutation.isPending ? 'Creating...' : 'Create Template'}
         </Button>
-        <Button type="button" variant="secondary" size="lg" onClick={() => navigate({ to: '/lessons/templates', search: {} as any })}>
+        <Button type="button" variant="secondary" size="lg" onClick={() => navigate({ to: '/lessons/templates', search: {} as Record<string, unknown> })}>
           Cancel
         </Button>
       </div>