refactor(billing): derive subscription product credits from shared tier map

lib/polar-products.ts

@@ -3,23 +3,27 @@ import {
   normalizePublicTier,
 } from "./tier-credits";
 
+export const TIER_MONTHLY_CREDITS = {
+  ...PUBLIC_TIER_MONTHLY_CREDITS,
+} as const;
+
 export const SUBSCRIPTION_PRODUCTS = {
   starter: {
     polarProductId: "81b6de07-cd41-430f-bd54-f0e7072deec6",
     price: 8,
-    credits: 400,
+    credits: TIER_MONTHLY_CREDITS.starter,
     label: "Starter",
   },
   pro: {
     polarProductId: "efb5cdb6-2cd6-4861-9073-7b43e29bc9f5",
     price: 59,
-    credits: 3300,
+    credits: TIER_MONTHLY_CREDITS.pro,
     label: "Pro",
   },
   max: {
     polarProductId: "40b850a9-0a07-4284-a749-c410ef532e80",
     price: 119,
-    credits: 6700,
+    credits: TIER_MONTHLY_CREDITS.max,
     label: "Max",
   },
 } as const;
@@ -51,10 +55,6 @@ export const TOPUP_PRODUCTS = [
   },
 ] as const;
 
-export const TIER_MONTHLY_CREDITS = {
-  ...PUBLIC_TIER_MONTHLY_CREDITS,
-} as const;
-
 export function normalizeTier(tier: string | undefined | null): keyof typeof TIER_MONTHLY_CREDITS {
   return normalizePublicTier(tier);
 }