init: 后端框架脚手架 (Go + Gin + GORM + MySQL)

- 项目目录结构：backend/ deploy/ schema/ migrations/
- 数据库 Schema：所有建表 SQL，含 hotel_id 多租户隔离
- Go 后端：config、model、handler、service、middleware、router
- 认证：账号密码登录 + JWT（Access + Refresh Token）
- 许可证：HMAC-SHA256 激活码生成 + 设备绑定验证
- 业务模块：商品、仓库、往来单位、入库、出库、库存、盘点
- 库存事务：入库/出库审核时原子更新库存 + 流水记录
- 数据导入：Excel/CSV 批量导入商品、往来单位
- Docker Compose：本地 MySQL + Adminer

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/middleware/auth.go

@@ -0,0 +1,74 @@
+package middleware
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/golang-jwt/jwt/v5"
+	"github.com/wangjia/jiu/backend/config"
+)
+
+type Claims struct {
+	UserID  uint64 `json:"user_id"`
+	HotelID uint64 `json:"hotel_id"`
+	Role    string `json:"role"`
+	jwt.RegisteredClaims
+}
+
+const (
+	CtxUserID  = "user_id"
+	CtxHotelID = "hotel_id"
+	CtxRole    = "role"
+)
+
+func JWT() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		authHeader := c.GetHeader("Authorization")
+		if authHeader == "" || !strings.HasPrefix(authHeader, "Bearer ") {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "missing token"})
+			return
+		}
+
+		tokenStr := strings.TrimPrefix(authHeader, "Bearer ")
+		claims := &Claims{}
+		token, err := jwt.ParseWithClaims(tokenStr, claims, func(t *jwt.Token) (interface{}, error) {
+			return []byte(config.C.JWT.Secret), nil
+		})
+		if err != nil || !token.Valid {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid token"})
+			return
+		}
+
+		c.Set(CtxUserID, claims.UserID)
+		c.Set(CtxHotelID, claims.HotelID)
+		c.Set(CtxRole, claims.Role)
+		c.Next()
+	}
+}
+
+// AdminOnly 仅管理员可访问
+func AdminOnly() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		role, _ := c.Get(CtxRole)
+		if role != "admin" {
+			c.AbortWithStatusJSON(http.StatusForbidden, gin.H{"error": "admin only"})
+			return
+		}
+		c.Next()
+	}
+}
+
+// GetHotelID 从 context 中安全获取 hotel_id
+func GetHotelID(c *gin.Context) uint64 {
+	v, _ := c.Get(CtxHotelID)
+	id, _ := v.(uint64)
+	return id
+}
+
+// GetUserID 从 context 中安全获取 user_id
+func GetUserID(c *gin.Context) uint64 {
+	v, _ := c.Get(CtxUserID)
+	id, _ := v.(uint64)
+	return id
+}