feat(billing): integrate Stripe for subscription management and billing access

- Added billing-related fields to the User model in the database.
- Implemented functions for managing billing access, including trial periods and subscription statuses.
- Created new billing utility functions for Stripe integration.
- Updated onboarding page to include billing overview and workspace creation eligibility.
- Enhanced route access checks to require billing access for certain actions.
- Implemented cleanup scripts for expired billing workspaces and associated media.
- Updated header component to conditionally show app navigation based on billing access.
- Added new migrations for billing-related database changes.

lib/stripe.ts

@@ -0,0 +1,38 @@
+import Stripe from 'stripe';
+
+let stripeClient: Stripe | null = null;
+
+export function isStripeConfigured() {
+  return Boolean(process.env.STRIPE_SECRET_KEY && process.env.STRIPE_PRICE_ID);
+}
+
+export function getStripe() {
+  const secretKey = process.env.STRIPE_SECRET_KEY;
+  if (!secretKey) {
+    throw new Error('STRIPE_SECRET_KEY is not configured');
+  }
+
+  if (!stripeClient) {
+    stripeClient = new Stripe(secretKey);
+  }
+
+  return stripeClient;
+}
+
+export function getStripePriceId() {
+  const priceId = process.env.STRIPE_PRICE_ID;
+  if (!priceId) {
+    throw new Error('STRIPE_PRICE_ID is not configured');
+  }
+
+  return priceId;
+}
+
+export function getStripeWebhookSecret() {
+  const webhookSecret = process.env.STRIPE_WEBHOOK_SECRET;
+  if (!webhookSecret) {
+    throw new Error('STRIPE_WEBHOOK_SECRET is not configured');
+  }
+
+  return webhookSecret;
+}