chore: Remove unused billing-related collections, types, and utility modules

- Drop `customers` collection and associated types (`types/index.ts`, `payload.ts`)
- Remove generated `payload-types.ts` file
- Clean up unused exports and dependencies across modules
- Streamline codebase by eliminating redundant billing logic

src/plugin/index.ts

@@ -0,0 +1,70 @@
+import type { Config } from 'payload'
+import { createInvoicesCollection, createPaymentsCollection, createRefundsCollection } from '@/collections'
+import { BillingPluginConfig } from '@/plugin/config'
+
+export const billingPlugin = (pluginConfig: BillingPluginConfig = {}) => (config: Config): Config => {
+  if (pluginConfig.disabled) {
+    return config
+  }
+
+  // Initialize collections
+  if (!config.collections) {
+    config.collections = []
+  }
+
+  const customerSlug = pluginConfig.collections?.customers || 'customers'
+
+  config.collections.push(
+    createPaymentsCollection(pluginConfig.collections?.payments || 'payments'),
+    createInvoicesCollection(
+      pluginConfig.collections?.invoices || 'invoices',
+      pluginConfig.collections?.customerRelation !== false ? customerSlug : undefined,
+      pluginConfig.customerInfoExtractor
+    ),
+    createRefundsCollection(pluginConfig.collections?.refunds || 'refunds'),
+  )
+
+  // Initialize endpoints
+  if (!config.endpoints) {
+    config.endpoints = []
+  }
+
+  config.endpoints?.push(
+    // Webhook endpoints
+    {
+      handler: (_req) => {
+        try {
+          const provider = null
+          if (!provider) {
+            return Response.json({ error: 'Provider not found' }, { status: 404 })
+          }
+
+          // TODO: Process webhook event and update database
+
+          return Response.json({ received: true })
+        } catch (error) {
+          // TODO: Use proper logger instead of console
+          // eslint-disable-next-line no-console
+          console.error('[BILLING] Webhook error:', error)
+          return Response.json({ error: 'Webhook processing failed' }, { status: 400 })
+        }
+      },
+      method: 'post',
+      path: '/billing/webhooks/:provider'
+    },
+  )
+
+  // Initialize providers and onInit hook
+  const incomingOnInit = config.onInit
+
+  config.onInit = async (payload) => {
+    // Execute any existing onInit functions first
+    if (incomingOnInit) {
+      await incomingOnInit(payload)
+    }
+
+  }
+
+  return config
+}
+export default billingPlugin