Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/actions/voucher.ts

@@ -23,10 +23,7 @@ export type RedeemState = { ok: boolean; message: string } | null;
  * voucher schema carries a single `amount`, granted as the website credits
  * wallet currency.
  */
-export async function redeem(
-  _prev: RedeemState,
-  formData: FormData,
-): Promise<RedeemState> {
+export async function redeem(_prev: RedeemState, formData: FormData): Promise<RedeemState> {
   const session = await auth();
   if (!session?.user?.id) {
     return { ok: false, message: "You must be signed in to redeem a voucher." };