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/service/migrate.go

@@ -0,0 +1,51 @@
+package service
+
+import (
+	"log"
+
+	"gorm.io/gorm"
+
+	"github.com/wangjia/jiu/backend/internal/model"
+)
+
+// BackfillPricingColumns 2026-07 定价字段消歧的一次性数据迁移（幂等，可反复执行）：
+//   - stock_in_items / stock_out_items：unit_price→cost_price、total_price→cost_amount
+//   - stock_in_orders：total_amount→cost_total；stock_out_orders：total_amount→sale_total
+//   - stock_out_items.sale_amount = sale_price×quantity（待定价行保持 0）
+//   - stock_out_orders.profit_total = Σ(sale_price>0 ? (sale_price-cost_price)×qty : 0)
+//
+// 只在新列为 0 且旧列非 0 时拷贝，不修改旧列（旧列观察一版后手动 DROP）。
+// profit_total 以「为 0 且存在已定价明细」为待回填判据——利润恰为 0 的单重算一次
+// 结果不变，幂等。全新安装（schema.sql 已无旧列）时整体跳过。
+func BackfillPricingColumns(db *gorm.DB) {
+	// 旧列存在性守卫：四张表的旧列是同批产生的，抽查一张即可
+	// （model 已无 UnitPrice 字段，HasColumn 会按原始列名探测）
+	if !db.Migrator().HasColumn(&model.StockOutItem{}, "unit_price") {
+		return
+	}
+	stmts := []string{
+		`UPDATE stock_in_items SET cost_price = unit_price WHERE cost_price = 0 AND unit_price <> 0`,
+		`UPDATE stock_in_items SET cost_amount = total_price WHERE cost_amount = 0 AND total_price <> 0`,
+		`UPDATE stock_in_orders SET cost_total = total_amount WHERE cost_total = 0 AND total_amount <> 0`,
+		`UPDATE stock_out_items SET cost_price = unit_price WHERE cost_price = 0 AND unit_price <> 0`,
+		`UPDATE stock_out_items SET cost_amount = total_price WHERE cost_amount = 0 AND total_price <> 0`,
+		`UPDATE stock_out_items SET sale_amount = sale_price * quantity WHERE sale_amount = 0 AND sale_price > 0`,
+		`UPDATE stock_out_orders SET sale_total = total_amount WHERE sale_total = 0 AND total_amount <> 0`,
+		`UPDATE stock_out_orders SET profit_total = (
+			SELECT COALESCE(SUM(CASE WHEN i.sale_price > 0
+				THEN (i.sale_price - i.cost_price) * i.quantity ELSE 0 END), 0)
+			FROM stock_out_items i WHERE i.order_id = stock_out_orders.id
+		) WHERE profit_total = 0 AND EXISTS (
+			SELECT 1 FROM stock_out_items i2
+			WHERE i2.order_id = stock_out_orders.id AND i2.sale_price > 0
+		)`,
+	}
+	for _, q := range stmts {
+		res := db.Exec(q)
+		if res.Error != nil {
+			log.Printf("backfill pricing columns failed (%.60s...): %v", q, res.Error)
+		} else if res.RowsAffected > 0 {
+			log.Printf("backfill pricing: %d rows (%.60s...)", res.RowsAffected, q)
+		}
+	}
+}