feat: 增加规格匹配建议与决策审计 (#90)

docs/admin/03-data-model.md

@@ -599,6 +599,38 @@ OptionKey(map[string]string{"size": "M", "color": "黑色"})
 只要有一点点不同（空格、转义、键序），映射就会静默对不上。
 **Client 只上报 `options` 对象，key 一律由 Admin 这一个函数算。**
 
+### 6.3 `spec_mapping_decisions` 决策审计
+
+本表只追加、不参与业务判断。每次成功保存映射时，与 `spec_mappings` 在同一事务写入；
+没有建议时 `suggested_option_key` 为 NULL 且 `accepted=0`。`accepted=0` 表示未采纳建议或当时无建议。
+
+```sql
+CREATE TABLE spec_mapping_decisions (
+    id BIGINT AUTO_INCREMENT PRIMARY KEY,
+    shopee_goods_id VARCHAR(191) COLLATE utf8mb4_bin NOT NULL,
+    spec_key VARCHAR(191) COLLATE utf8mb4_bin NOT NULL,
+    pdd_goods_id VARCHAR(191) COLLATE utf8mb4_bin NOT NULL,
+    rules_version VARCHAR(32) NOT NULL,
+    suggested_option_key VARCHAR(191) COLLATE utf8mb4_bin,
+    chosen_option_key VARCHAR(191) COLLATE utf8mb4_bin NOT NULL,
+    accepted TINYINT NOT NULL CHECK (accepted IN (0, 1)),
+    decided_by VARCHAR(191),
+    decided_at VARCHAR(35) NOT NULL,
+    KEY idx_decisions_mapping (shopee_goods_id, spec_key, pdd_goods_id)
+);
+```
+
+下面的指标只能称为“成功保存决策中的建议采纳率”，不是准确率：
+
+```sql
+SELECT rules_version, COUNT(*) AS 有建议的决策数, SUM(accepted) AS 采纳数,
+       ROUND(SUM(accepted) / COUNT(*) * 100, 1) AS 采纳率
+FROM spec_mapping_decisions WHERE suggested_option_key IS NOT NULL GROUP BY rules_version;
+
+SELECT rules_version, COUNT(*) AS 无建议决策数
+FROM spec_mapping_decisions WHERE suggested_option_key IS NULL GROUP BY rules_version;
+```
+
 ## 7. `tasks` 任务
 
 采集任务和采购任务共用一张表，用 `task_type` 区分。