feat(backend): 出入库定价字段消歧 + 总利润落库 + 成本仅管理员可见

- 字段重命名（旧列弃用保留，启动幂等回填 BackfillPricingColumns）：
  入库 unit_price/total_price/total_amount → cost_price/cost_amount/cost_total；
  出库同前缀 + 新增 sale_amount（售价小计）/ sale_total（应收）/ profit_total（总利润）
- 建单落三值；确认售价联动重算 sale_amount/sale_total/profit_total；
  确认进价回填成本后联动重算受影响出库单利润（recalcStockOutProfit）
- 出库 List/Get 对 operator/readonly 抹零成本与利润（stripStockOutCost 服务端兜底）
- 兼容一版：Create/Update 接受旧 key unit_price 回落（v1.0.87 及之前客户端）
- SUM 聚合/价格趋势/导入/种子工具同步切新列；测试全量改名 + 6 个新回归

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

backend/internal/handler/stock_in_test.go

@@ -402,6 +402,7 @@ func TestStockInHandler_TotalAmount(t *testing.T) {
 	w := makeRequest(r, "POST", "/api/v1/stock-in/orders", token, map[string]interface{}{
 		"warehouse_id": warehouse.ID,
 		"order_date":   time.Now().Format(time.RFC3339),
+		// 故意发旧 key unit_price：v1.0.87 及之前客户端的兼容回归（回落到 cost_price）
 		"items": []map[string]interface{}{
 			{"product_id": product1.ID, "quantity": 10.0, "unit_price": 5.0}, // 50
 			{"product_id": product2.ID, "quantity": 3.0, "unit_price": 20.0}, // 60
@@ -409,7 +410,7 @@ func TestStockInHandler_TotalAmount(t *testing.T) {
 	})
 	require.Equal(t, http.StatusCreated, w.Code)
 	data := parseResponse(w)["data"].(map[string]interface{})
-	assert.Equal(t, float64(110), data["total_amount"])
+	assert.Equal(t, float64(110), data["cost_total"])
 }
 
 // 回归：编辑草稿入库单后 total_amount 必须按新明细重算（此前 Update 漏了累加，编辑后被清成 0）。
@@ -437,8 +438,8 @@ func TestStockInHandler_UpdateRecomputesTotal(t *testing.T) {
 		"warehouse_id": warehouse.ID,
 		"order_date":   time.Now().Format(time.RFC3339),
 		"items": []map[string]interface{}{
-			{"product_name": "茅台2009", "series": "大件", "spec": "500ml", "quantity": 12.0, "unit_price": 3100.0},
-			{"product_name": "茅台十五年", "series": "大件", "spec": "500ml", "quantity": 1.0, "unit_price": 4500.0},
+			{"product_name": "茅台2009", "series": "大件", "spec": "500ml", "quantity": 12.0, "cost_price": 3100.0},
+			{"product_name": "茅台十五年", "series": "大件", "spec": "500ml", "quantity": 1.0, "cost_price": 4500.0},
 		},
 	})
 	require.Equal(t, http.StatusOK, w.Code)
@@ -447,7 +448,7 @@ func TestStockInHandler_UpdateRecomputesTotal(t *testing.T) {
 	w = makeRequest(r, "GET", fmt.Sprintf("/api/v1/stock-in/orders/%d", orderID), token, nil)
 	require.Equal(t, http.StatusOK, w.Code)
 	data := parseResponse(w)["data"].(map[string]interface{})
-	assert.Equal(t, float64(41700), data["total_amount"], "编辑后金额应按新明细重算")
+	assert.Equal(t, float64(41700), data["cost_total"], "编辑后金额应按新明细重算")
 }
 
 func TestStockInHandler_NoAuth(t *testing.T) {