feat(ECR-018): Entitlement 用户权益只读并 Closed

聚合 GET /admin/users/:id/entitlements（Membership∪DeepAccess∪问答额度）与 admin-h5 权益 Tab；无 migration / 无真支付。

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/BACKEND_DESIGN/BD-2026-018-entitlement.md

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+# Backend Design: ECR-018 Entitlement
+
+| ID | BD-2026-018 |
+| Status | Approved |
+| Coding | Loop authorized |
+| Level | L2 |
+| Migration | NO |
+
+## Backend Change Boundary
+
+```text
+Domain: Entitlement read model (Membership ∪ DeepAccess ∪ ask quotas)
+App: AdminHandler → admin.Service → AdminRepo + ReportRepo.GetMembership
+API: GET /api/v1/admin/users/{id}/entitlements
+Permission: admin.users.read
+Migration: NO
+UI: admin-h5 UserDetail「权益」Tab
+```
+
+## Out of boundary
+
+Payment gateway · new entitlement matrix table · order mutation · UGC
+
+Rollback: remove route + UI tab（无 schema）