fix(plan): drop the redundant 'Zrušit' button in the category-management modal

The Správa kategorií modal footer had two buttons that both just close it (Zrušit + Zavřít). Added an opt-in hideCancel prop to the kit Modal (default false → every other modal unchanged) and set it on PlanCategoriesModal, leaving only 'Zavřít'. Verified: footer shows only Zavřít; close/Escape/backdrop intact.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/components/PlanCategoriesModal.tsx

@@ -107,6 +107,7 @@ export default function PlanCategoriesModal({
       onSubmit={onClose}
       title="Správa kategorií"
       submitText="Zavřít"
+      hideCancel
       maxWidth="md"
     >
       <Box>