feat: implement one-time admin token generation and upgrade process

src/app/actions/verify-admin-token.ts

@@ -0,0 +1,14 @@
+'use server';
+
+export async function verifyAdminToken(token: string): Promise<{ valid: boolean }> {
+  const storedToken = process.env.ADMIN_SIGNUP_TOKEN;
+  
+  // Token is invalid if:
+  // 1. No token exists (already used or no token was generated)
+  // 2. Provided token doesn't match
+  if (!storedToken || token !== storedToken) {
+    return { valid: false };
+  }
+
+  return { valid: true };
+}