Remove billing and checkout redirect buttons and related services

Deleted the billing-redirect-button, checkout-redirect-button, and embedded-stripe-checkout components. Additionally, removed the shadcn directory, which encompassed billing-related icons. This change streamlines the subscription settings interface and organizes the system's payment management. This update is a stepping stone towards improving the billing system's overall architecture.

packages/billing/src/services/billing-webhook-handler.service.ts

@@ -0,0 +1,32 @@
+import { Database } from '@kit/supabase/database';
+
+type SubscriptionObject = Database['public']['Tables']['subscriptions'];
+
+type SubscriptionInsertParams = Omit<
+  SubscriptionObject['Insert'],
+  'billing_customer_id'
+>;
+
+type SubscriptionUpdateParams = SubscriptionObject['Update'];
+
+/**
+ * Represents an abstract class for handling billing webhook events.
+ */
+export abstract class BillingWebhookHandlerService {
+  abstract verifyWebhookSignature(request: Request): Promise<unknown>;
+
+  abstract handleWebhookEvent(
+    event: unknown,
+    params: {
+      onCheckoutSessionCompleted: (
+        subscription: SubscriptionInsertParams,
+      ) => Promise<unknown>;
+
+      onSubscriptionUpdated: (
+        subscription: SubscriptionUpdateParams,
+      ) => Promise<unknown>;
+
+      onSubscriptionDeleted: (subscriptionId: string) => Promise<unknown>;
+    },
+  ): Promise<unknown>;
+}