feat: add new subscription tier and update credit configurations

- Introduced a new "max" subscription tier with associated monthly credits and top-up limits.
- Updated existing subscription tiers' monthly credits and top-up limits for "starter", "pro", and "business".
- Enhanced credit display and overview components to reflect the new tier and its attributes.
- Integrated Polar authentication features for improved subscription management and credit handling.

lib/ai-models.ts

@@ -9,7 +9,7 @@ export interface AiModel {
   estimatedCost: string; // human-readable, e.g. "~€0.04"
   /** Credits pro Generierung — gleiche Einheit wie Convex reserve/commit (Euro-Cent). */
   creditCost: number;
-  minTier: "free" | "starter" | "pro" | "business"; // minimum subscription tier
+  minTier: "free" | "starter" | "pro" | "max" | "business"; // minimum subscription tier
 }
 
 export const IMAGE_MODELS: AiModel[] = [

lib/auth-client.ts

@@ -1,7 +1,8 @@
 import { createAuthClient } from "better-auth/react";
 import { convexClient } from "@convex-dev/better-auth/client/plugins";
+import { polarClient } from "@polar-sh/better-auth/client";
 
 // Next.js: kein crossDomainClient nötig (same-origin via API Route Proxy)
 export const authClient = createAuthClient({
-  plugins: [convexClient()],
+  plugins: [convexClient(), polarClient()],
 });

lib/polar-products.ts

@@ -0,0 +1,61 @@
+export const SUBSCRIPTION_PRODUCTS = {
+  starter: {
+    polarProductId: "81b6de07-cd41-430f-bd54-f0e7072deec6",
+    price: 8,
+    credits: 400,
+    label: "Starter",
+  },
+  pro: {
+    polarProductId: "efb5cdb6-2cd6-4861-9073-7b43e29bc9f5",
+    price: 59,
+    credits: 3300,
+    label: "Pro",
+  },
+  max: {
+    polarProductId: "40b850a9-0a07-4284-a749-c410ef532e80",
+    price: 119,
+    credits: 6700,
+    label: "Max",
+  },
+} as const;
+
+export const TOPUP_PRODUCTS = [
+  {
+    label: "Klein",
+    price: 5,
+    credits: 250,
+    polarProductId: "539a18b1-375c-4d70-ae84-66c53cb365f8",
+  },
+  {
+    label: "Mittel",
+    price: 10,
+    credits: 500,
+    polarProductId: "d62970e4-fb5a-4f72-b4af-1bb92a575fa8",
+  },
+  {
+    label: "Groß",
+    price: 20,
+    credits: 1000,
+    polarProductId: "ed4f0c05-7d77-4087-bcf7-cf60174e1316",
+  },
+  {
+    label: "XL",
+    price: 50,
+    credits: 3000,
+    polarProductId: "79a27a33-e8bf-4205-b37b-b9431593310b",
+  },
+] as const;
+
+export const TIER_MONTHLY_CREDITS = {
+  free: 50,
+  starter: 400,
+  pro: 3300,
+  max: 6700,
+} as const;
+
+export function normalizeTier(tier: string | undefined | null): keyof typeof TIER_MONTHLY_CREDITS {
+  if (!tier || tier === "free") return "free";
+  if (tier === "starter" || tier === "pro" || tier === "max") return tier;
+  if (tier === "business") return "max";
+  return "free";
+}

lib/topup-calculator.ts

@@ -0,0 +1,14 @@
+export function calculateCustomTopup(euroAmount: number): {
+  credits: number;
+  bonusRate: number;
+} {
+  const bonusRate =
+    euroAmount >= 100 ? 0.13 :
+    euroAmount >= 50 ? 0.10 :
+    euroAmount >= 20 ? 0.06 :
+    euroAmount >= 10 ? 0.03 : 0;
+
+  const netAmount = euroAmount / 1.19;
+  const credits = Math.floor((netAmount * 0.70 * (1 + bonusRate)) / 0.01);
+  return { credits, bonusRate };
+}