fix: align superadmin sort fields

docs/backend_sort_alignment_plan.md

@@ -0,0 +1,79 @@
+# Backend Sort Alignment Plan (Superadmin)
+
+## Goal
+Align backend sort support with the superadmin UI for the following lists:
+- Tenants list: `user_count`, `income_amount_paid_sum`
+- Balance anomalies: `user_id`, `created_at`
+- Order anomalies: `order_id`
+
+## Scope
+- Backend services only (no UI changes).
+- Sorting behavior and documentation updates.
+- Add service-level tests to cover the new sort fields.
+
+## Non-Goals
+- Changing pagination logic or query filters.
+- Adding new UI sorting fields.
+- Changing business semantics of existing aggregates.
+
+## Proposed Approach
+### 1) Tenants list sorting (已完成)
+Backend: `services.Super.ListTenants`
+
+Add two aggregate subqueries and join them for ordering:
+- `user_count`
+  - `tenant_users` aggregate: `SELECT tenant_id, COUNT(*) AS user_count FROM tenant_users GROUP BY tenant_id`
+- `income_amount_paid_sum`
+  - `orders` aggregate: `SELECT tenant_id, COALESCE(SUM(amount_paid), 0) AS income_amount_paid_sum FROM orders WHERE status IN (paid, refunding, refunded) GROUP BY tenant_id`
+
+Ordering behavior:
+- Extend the sort switch to accept `user_count` and `income_amount_paid_sum`.
+- Map sort to the joined aggregate columns (use `COALESCE` to avoid null ordering issues).
+
+Count safety:
+- Keep `Count()` on the base tenant query or use `COUNT(DISTINCT tenants.id)` after joins to avoid inflation.
+- Apply joins only for the query that fetches paged data when possible.
+
+### 2) Balance anomalies sorting (已完成)
+Backend: `services.Super.ListBalanceAnomalies`
+
+Extend sort switch:
+- `user_id` -> `tbl.ID`
+- `created_at` -> `tbl.CreatedAt`
+
+### 3) Order anomalies sorting (已完成)
+Backend: `services.Super.ListOrderAnomalies`
+
+Extend sort switch:
+- `order_id` -> `tbl.ID`
+
+### 4) Documentation updates (DTO comments) (已完成)
+Update sort field documentation to reflect new options:
+- `TenantListFilter` (add `user_count`, `income_amount_paid_sum`)
+- `SuperBalanceAnomalyFilter` (add `user_id`, `created_at`)
+- `SuperOrderAnomalyFilter` (add `order_id`)
+
+## Tests (已完成)
+Add service-level tests (in `backend/app/services/super_test.go` or a new test file):
+- Tenants list sorting:
+  - Create tenants with different member counts and income sums.
+  - Verify `asc`/`desc` on `user_count` and `income_amount_paid_sum`.
+- Balance anomalies sorting:
+  - Create users with negative balances and controlled `created_at`.
+  - Verify `asc`/`desc` on `created_at` and `user_id`.
+- Order anomalies sorting:
+  - Create anomaly orders with distinct IDs.
+  - Verify ordering by `order_id`.
+
+Run:
+- `go test ./...`
+
+## Files to Change
+- `backend/app/services/super.go`
+- `backend/app/http/super/v1/dto/super.go`
+- `backend/app/http/super/v1/dto/super_finance.go`
+- `backend/app/services/super_test.go` (or new test file)
+
+## Risks / Notes
+- Join-based sorting can impact performance on large tables; consider indexes on `tenant_users.tenant_id` and `orders.tenant_id`.
+- Ensure aggregate semantics match current `buildTenantItems` logic to keep UI numbers consistent.