feat: disallow double lifetime buys

apps/pay/src/routes.ts

@@ -60,10 +60,12 @@ export const routes = new Elysia()
 
     const { plan, months, coin } = body;
 
-    // Validate plan
+    // Validate plan — block duplicate lifetime
     if (plan === "lifetime") {
-      const [acc] = await sql`SELECT plan FROM accounts WHERE id = ${accountId}`;
-      if (acc.plan === "lifetime") { set.status = 400; return { error: "Already on lifetime plan" }; }
+      const [acc] = await sql`SELECT plan, plan_stack FROM accounts WHERE id = ${accountId}`;
+      const stack = typeof acc.plan_stack === "string" ? JSON.parse(acc.plan_stack) : (acc.plan_stack || []);
+      const hasLifetime = acc.plan === "lifetime" || stack.some((s: any) => s.plan === "lifetime");
+      if (hasLifetime) { set.status = 400; return { error: "You already have a lifetime plan" }; }
     }
 
     // Validate coin