feat(backend): 库存三态落库（stock/on_sale/sold）——挂售可控 + 卖光留痕

- inventories 加 status 枚举列（默认 stock，AutoMigrate 存量即全部「库存」）+ 索引
- 出库审核扣光置 sold 不再软删（留痕台账）；退单恢复行置回 stock；盘亏仍软删
- 新接口 PUT /inventory/:id/status（仅收 stock/on_sale，已售行拒改，租户校验）
- List 默认排除已售（显式 status=sold 才显示）+ status 多值筛选
- Summary：SKU/货值/数量排除已售，新增 sold_count
- 公开店铺页/API 只列 on_sale——酒单从全量裸奔改为人工精选
- 测试：卖光置售/部分不改/退单回库/接口边界/跨租户/汇总口径 8 用例
- 设计方案 docs/design/inventory-sale-status.html + db-schema/CLAUDE.md 同步

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJ1g8XV1YhhmHRzhwWEW7o

backend/internal/handler/inventory_test.go

@@ -442,3 +442,86 @@ func TestInventoryHandler_CostVisibility(t *testing.T) {
 		assert.Equal(t, float64(10), resp["in_stock_qty"].(float64))
 	}
 }
+
+// 库存三态（2026-07-07）：List 默认排除已售、status 筛选、切换接口、Summary sold_count。
+func TestInventoryHandler_StatusFlow(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "INV_ST")
+	user := testutil.CreateTestUser(db, shop.ID, "admin", "pass", "admin")
+	wh := testutil.CreateTestWarehouse(db, shop.ID, "仓")
+	p1 := testutil.CreateTestProduct(db, shop.ID, "库存酒")
+	p2 := testutil.CreateTestProduct(db, shop.ID, "在售酒")
+	p3 := testutil.CreateTestProduct(db, shop.ID, "已售酒")
+	token := getAuthToken(user.ID, shop.ID, "admin")
+	r := setupProtectedRouter(db)
+
+	price := 50.0
+	invStock := model.Inventory{ShopID: shop.ID, WarehouseID: &wh.ID, ProductID: &p1.ID, Quantity: 3, UnitPrice: &price, Status: "stock"}
+	invSale := model.Inventory{ShopID: shop.ID, WarehouseID: &wh.ID, ProductID: &p2.ID, Quantity: 2, UnitPrice: &price, Status: "on_sale"}
+	invSold := model.Inventory{ShopID: shop.ID, WarehouseID: &wh.ID, ProductID: &p3.ID, Quantity: 0, UnitPrice: &price, Status: "sold"}
+	require.NoError(t, db.Create(&invStock).Error)
+	require.NoError(t, db.Create(&invSale).Error)
+	require.NoError(t, db.Create(&invSold).Error)
+
+	// List 默认：不含已售（2 行）
+	w := makeRequest(r, "GET", "/api/v1/inventory", token, nil)
+	assert.Equal(t, float64(2), parseResponse(w)["total"].(float64))
+
+	// status=sold：只看已售
+	w = makeRequest(r, "GET", "/api/v1/inventory?status=sold", token, nil)
+	resp := parseResponse(w)
+	assert.Equal(t, float64(1), resp["total"].(float64))
+	row := resp["data"].([]interface{})[0].(map[string]interface{})
+	assert.Equal(t, "sold", row["status"])
+
+	// status 多值
+	w = makeRequest(r, "GET", "/api/v1/inventory?status=stock,on_sale,sold", token, nil)
+	assert.Equal(t, float64(3), parseResponse(w)["total"].(float64))
+
+	// 切换：stock → on_sale
+	w = makeRequest(r, "PUT", fmt.Sprintf("/api/v1/inventory/%d/status", invStock.ID), token,
+		map[string]interface{}{"status": "on_sale"})
+	assert.Equal(t, http.StatusOK, w.Code)
+	var got model.Inventory
+	require.NoError(t, db.Where("id = ?", invStock.ID).First(&got).Error)
+	assert.Equal(t, "on_sale", got.Status)
+
+	// 拒收 sold 值
+	w = makeRequest(r, "PUT", fmt.Sprintf("/api/v1/inventory/%d/status", invSale.ID), token,
+		map[string]interface{}{"status": "sold"})
+	assert.Equal(t, http.StatusBadRequest, w.Code)
+
+	// 已售行不可改
+	w = makeRequest(r, "PUT", fmt.Sprintf("/api/v1/inventory/%d/status", invSold.ID), token,
+		map[string]interface{}{"status": "stock"})
+	assert.Equal(t, http.StatusNotFound, w.Code)
+
+	// Summary：sku_count 排除已售、sold_count=1、货值只算未售
+	w = makeRequest(r, "GET", "/api/v1/inventory/summary", token, nil)
+	sm := parseResponse(w)
+	assert.Equal(t, float64(2), sm["sku_count"].(float64))
+	assert.Equal(t, float64(1), sm["sold_count"].(float64))
+	assert.Equal(t, float64(3*50+2*50), sm["stock_value"].(float64))
+	assert.Equal(t, float64(0), sm["shortage_count"].(float64), "sold 不计入缺货")
+}
+
+// 跨租户：不能改他店库存状态
+func TestInventoryHandler_StatusTenantIsolation(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shopA := testutil.CreateTestShop(db, "INV_STA")
+	shopB := testutil.CreateTestShop(db, "INV_STB")
+	userA := testutil.CreateTestUser(db, shopA.ID, "admin", "pass", "admin")
+	whB := testutil.CreateTestWarehouse(db, shopB.ID, "仓B")
+	pB := testutil.CreateTestProduct(db, shopB.ID, "他店酒")
+	invB := model.Inventory{ShopID: shopB.ID, WarehouseID: &whB.ID, ProductID: &pB.ID, Quantity: 1, Status: "stock"}
+	require.NoError(t, db.Create(&invB).Error)
+	r := setupProtectedRouter(db)
+
+	tokenA := getAuthToken(userA.ID, shopA.ID, "admin")
+	w := makeRequest(r, "PUT", fmt.Sprintf("/api/v1/inventory/%d/status", invB.ID), tokenA,
+		map[string]interface{}{"status": "on_sale"})
+	assert.Equal(t, http.StatusNotFound, w.Code)
+	var got model.Inventory
+	require.NoError(t, db.Where("id = ?", invB.ID).First(&got).Error)
+	assert.Equal(t, "stock", got.Status)
+}