fix: restrict only a seller can create a custom store front

[levalleux-ludo]

No description provided.

[albertfolch-redeemeum]

FYI this is somehow implemented in

interface/src/pages/custom-store/CustomStorePage.tsx

Lines 73 to 79 in 94b2f69

	if (!seller) {
	return (
	<div data-testid="notFound">
	No seller account found for the current wallet.
	</div>
	);
	}