chore: relocate backend into apps/api ahead of monorepo merge

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/routes/client/course_purchases.routes.js

@@ -0,0 +1,10 @@
+const express = require('express');
+const router  = express.Router();
+const ctrl    = require('../../controllers/client/course_purchases.controller');
+
+router.get ('/',         ctrl.getMyPurchases);
+router.post('/order',    ctrl.createCourseOrder);
+router.post('/capture',  ctrl.captureCourseOrder);
+router.post('/cancel',   ctrl.cancelCourseOrder);
+
+module.exports = router;