feat(backend): license_purchases 增 amount_minor/currency/pay_url/renewed_to 列 + 存量回填（pay v2 金额口径）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/service/pay.go

@@ -368,6 +368,21 @@ func entitle(tx *gorm.DB, shopID uint64, plan payPlan) error {
 	}).Error
 }
 
+// BackfillPurchaseAmountMinor 启动回填：v1 存量购买单 amount("2999.00") → amount_minor(299900)+CNY。
+// 幂等：只处理 amount_minor=0 且 amount 非空的行（参照 backfillPinyin 先例）。
+func BackfillPurchaseAmountMinor(db *gorm.DB) {
+	var rows []model.LicensePurchase
+	if err := db.Where("amount_minor = 0 AND amount <> ''").Find(&rows).Error; err != nil {
+		return
+	}
+	for _, p := range rows {
+		if c, err := toCents(p.Amount); err == nil && c > 0 {
+			db.Model(&model.LicensePurchase{}).Where("id = ?", p.ID).
+				Updates(map[string]any{"amount_minor": c, "currency": "CNY"})
+		}
+	}
+}
+
 // amountEqual 金额按分归一比较（"2999.00" == "2999" == "2999.0"）。
 func amountEqual(a, b string) bool {
 	ca, ea := toCents(a)

backend/internal/service/pay_test.go

@@ -370,3 +370,30 @@ func TestStatus_ScopedToShop(t *testing.T) {
 	_, err = svc.Status(other.ID, "yanmei-otn-7")
 	assert.ErrorIs(t, err, ErrPurchaseNotFound, "跨店不可见")
 }
+
+// ---------- v2 金额回填 ----------
+
+func TestBackfillPurchaseAmountMinor(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY012")
+
+	p1 := createPendingPurchase(t, db, shop.ID, "annual_standard", "2999.00", "yanmei-backfill-1")
+	p2 := createPendingPurchase(t, db, shop.ID, PromoBizCode, "1.00", "yanmei-backfill-2")
+	// 已有 amount_minor>0 的行不应被覆盖
+	p3 := createPendingPurchase(t, db, shop.ID, "monthly_pro", "599.00", "yanmei-backfill-3")
+	require.NoError(t, db.Model(p3).Updates(map[string]any{"amount_minor": 123, "currency": "USD"}).Error)
+
+	BackfillPurchaseAmountMinor(db)
+
+	var got1, got2, got3 model.LicensePurchase
+	require.NoError(t, db.First(&got1, p1.ID).Error)
+	require.NoError(t, db.First(&got2, p2.ID).Error)
+	require.NoError(t, db.First(&got3, p3.ID).Error)
+
+	assert.Equal(t, int64(299900), got1.AmountMinor)
+	assert.Equal(t, "CNY", got1.Currency)
+	assert.Equal(t, int64(100), got2.AmountMinor)
+	assert.Equal(t, "CNY", got2.Currency)
+	assert.Equal(t, int64(123), got3.AmountMinor, "已有 amount_minor>0 的行不被覆盖")
+	assert.Equal(t, "USD", got3.Currency, "已有 amount_minor>0 的行不被覆盖")
+}