fix: unify handler response format in user_handler.go

- List/Get/Update/Delete users: standardize to {code, message, data} format
- UpdateUserStatus: standardize to {code, message} format
- handleError: standardize to {code, message} format (was {error: ...})
- All inline bad request errors now use {code: 400, message: ...} consistently

internal/api/handler/user_handler.go

@@ -102,17 +102,21 @@ func (h *UserHandler) ListUsers(c *gin.Context) {
 	}
 
 	c.JSON(http.StatusOK, gin.H{
-		"users":  userResponses,
-		"total":  total,
-		"offset": offset,
-		"limit":  limit,
+		"code":    0,
+		"message": "success",
+		"data": gin.H{
+			"users":  userResponses,
+			"total":  total,
+			"offset": offset,
+			"limit":  limit,
+		},
 	})
 }
 
 func (h *UserHandler) GetUser(c *gin.Context) {
 	id, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user id"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid user id"})
 		return
 	}
 
@@ -122,13 +126,13 @@ func (h *UserHandler) GetUser(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, toUserResponse(user))
+	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "success", "data": toUserResponse(user)})
 }
 
 func (h *UserHandler) UpdateUser(c *gin.Context) {
 	id, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user id"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid user id"})
 		return
 	}
 
@@ -138,7 +142,7 @@ func (h *UserHandler) UpdateUser(c *gin.Context) {
 	}
 
 	if err := c.ShouldBindJSON(&req); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": err.Error()})
 		return
 	}
 
@@ -160,13 +164,13 @@ func (h *UserHandler) UpdateUser(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, toUserResponse(user))
+	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "success", "data": toUserResponse(user)})
 }
 
 func (h *UserHandler) DeleteUser(c *gin.Context) {
 	id, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user id"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid user id"})
 		return
 	}
 
@@ -175,13 +179,13 @@ func (h *UserHandler) DeleteUser(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, gin.H{"message": "user deleted"})
+	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "success"})
 }
 
 func (h *UserHandler) UpdatePassword(c *gin.Context) {
 	id, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user id"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid user id"})
 		return
 	}
 
@@ -191,7 +195,7 @@ func (h *UserHandler) UpdatePassword(c *gin.Context) {
 	}
 
 	if err := c.ShouldBindJSON(&req); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": err.Error()})
 		return
 	}
 
@@ -200,13 +204,13 @@ func (h *UserHandler) UpdatePassword(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, gin.H{"message": "密码修改成功"})
+	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "密码修改成功"})
 }
 
 func (h *UserHandler) UpdateUserStatus(c *gin.Context) {
 	id, err := strconv.ParseInt(c.Param("id"), 10, 64)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user id"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid user id"})
 		return
 	}
 
@@ -215,7 +219,7 @@ func (h *UserHandler) UpdateUserStatus(c *gin.Context) {
 	}
 
 	if err := c.ShouldBindJSON(&req); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": err.Error()})
 		return
 	}
 
@@ -230,7 +234,7 @@ func (h *UserHandler) UpdateUserStatus(c *gin.Context) {
 	case "disabled", "3":
 		status = domain.UserStatusDisabled
 	default:
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid status"})
+		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "invalid status"})
 		return
 	}
 
@@ -239,7 +243,7 @@ func (h *UserHandler) UpdateUserStatus(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, gin.H{"message": "status updated"})
+	c.JSON(http.StatusOK, gin.H{"code": 0, "message": "success"})
 }
 
 func (h *UserHandler) GetUserRoles(c *gin.Context) {