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/schema/schema.sql

@@ -414,6 +414,7 @@ CREATE TABLE IF NOT EXISTS `inventories` (
   `stock_in_item_id`    BIGINT UNSIGNED DEFAULT NULL,
   `inventory_check_id`  BIGINT UNSIGNED DEFAULT NULL,
   `quantity`            DECIMAL(12,3)   NOT NULL DEFAULT 0,
+  `status`              ENUM('stock','on_sale','sold') NOT NULL DEFAULT 'stock' COMMENT '库存/在售(公开)/已售(卖光留痕)',
   `product_code`        VARCHAR(50)     DEFAULT NULL,
   `product_name`        VARCHAR(200)    DEFAULT NULL,
   `series`              VARCHAR(100)    DEFAULT NULL,
@@ -434,7 +435,8 @@ CREATE TABLE IF NOT EXISTS `inventories` (
   KEY `idx_shop_wh_product` (`shop_id`, `warehouse_id`, `product_id`),
   KEY `idx_stock_in_item` (`stock_in_item_id`),
   KEY `idx_inventory_check` (`inventory_check_id`),
-  KEY `idx_deleted_at` (`deleted_at`)
+  KEY `idx_deleted_at` (`deleted_at`),
+  KEY `idx_inv_status` (`status`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='库存批次记录';
 
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