chore(frontend): unexport two ConfirmProvider-internal types

knip flags them: both are only referenced inside the file. Clearing them is what
makes the lint lane green enough to become a hard publish gate.

frontend/src/components/ConfirmProvider.tsx

@@ -10,7 +10,7 @@ import Modal from "./Modal";
 // confirms, because the second dialog's Cancel/Escape/backdrop is then indistinguishable from
 // a deliberate answer (the playlist delete used to read a dismissal as "delete here only" and
 // went ahead and deleted).
-export interface ConfirmOptions {
+interface ConfirmOptions {
   title?: string;
   message: ReactNode;
   confirmLabel?: string;
@@ -18,7 +18,7 @@ export interface ConfirmOptions {
   danger?: boolean;
 }
 
-export interface Choice {
+interface Choice {
   id: string;
   label: string;
   danger?: boolean;