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

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

apps/api/database/migrations/20270101000090-relax-user-tiers-active-per-plan.js

@@ -0,0 +1,38 @@
+'use strict';
+
+// Tier Plans v2: item-specific entitlement means two DIFFERENT plans at the
+// SAME tier slug (e.g. two separate Premium bundles) must be able to stay
+// concurrently active for one user, each governing its own distinct
+// user_tier_grants snapshot — buying a second Premium bundle must not just
+// extend the first one's expiry (see captureOrder in
+// controllers/client/tiers.controller.js).
+//
+// The old partial unique index (20270101000075) enforced "one active row per
+// (user_id, tier)", which blocks that. Replace it with "one active row per
+// (user_id, plan_id)" — still prevents accidentally double-purchasing/
+// double-granting the exact same plan concurrently, but allows multiple
+// plans at the same tier to coexist. NULL plan_id rows (admin-granted
+// tiers with no backing plan) are never considered equal to one another by
+// a unique index, so they're unaffected.
+//
+// NOT auto-run — do not execute against the shared dev/prod database without
+// explicit confirmation.
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.removeIndex('user_tiers', 'user_tiers_one_active_per_user_tier');
+    await queryInterface.addIndex('user_tiers', ['user_id', 'plan_id'], {
+      unique: true,
+      where: { status: 'active' },
+      name: 'user_tiers_one_active_per_user_plan',
+    });
+  },
+
+  async down(queryInterface) {
+    await queryInterface.removeIndex('user_tiers', 'user_tiers_one_active_per_user_plan');
+    await queryInterface.addIndex('user_tiers', ['user_id', 'tier'], {
+      unique: true,
+      where: { status: 'active' },
+      name: 'user_tiers_one_active_per_user_tier',
+    });
+  },
+};