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

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

apps/api/routes/client/tiers.routes.js

@@ -0,0 +1,30 @@
+const express     = require('express');
+const router      = express.Router();
+const ctrl        = require('../../controllers/client/tiers.controller');
+
+// My tier
+router.get ('/me',               ctrl.getMyTier);
+router.get ('/me/history',       ctrl.getMyTierHistory);
+
+// Plans
+router.get ('/plans',            ctrl.getPlans);
+
+// Promo code validation
+router.post('/promos/validate',  ctrl.validatePromo);
+
+// Checkout
+router.post('/checkout/order',   ctrl.createOrder);
+router.post('/checkout/capture', ctrl.captureOrder);
+router.post('/checkout/cancel',  ctrl.cancelOrder);
+router.post('/checkout/refund',  ctrl.refundOrder);
+
+// My payments
+router.get ('/me/payments',      ctrl.getMyPayments);
+
+// Tier categories (public — for course badge display)
+router.get ('/categories',       ctrl.getCategories);
+
+// System badges (public read for profile display)
+router.get ('/system-badges',    ctrl.getSystemBadges);
+
+module.exports = router;