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

eslint.config.js

@@ -44,6 +44,7 @@ export default [
       'perfectionist/sort-switch-case': 'off',
       'perfectionist/sort-union-types': 'off',
       'perfectionist/sort-variable-declarations': 'off',
+      'perfectionist/sort-intersection-types': 'off',
     },
   },
   {