feat: 外观设置后端持久化 + 保存按钮 + 跨浏览器同步

后端:
- User 模型新增 Preferences JSON 字段 (theme + login_style)
- 新增 GET/PUT /api/v1/user/preferences (auth) 个人偏好读写
- 新增 GET /api/v1/public/login-style (public) 登录页风格公开端点
- SQLite users 表手动添加 preferences 列

前端:
- AppearanceSettings 从后端加载偏好 + 保存按钮 + dirty 状态提示
- LoginPage 先从后端公开接口获取 login_style (跨浏览器一致)
- useLogin 登录成功后从后端加载偏好并应用主题
- 偏好同时存 localStorage(即时) + 后端DB(跨设备)

backend/internal/handler/preferences.go

@@ -0,0 +1,69 @@
+package handler
+
+import (
+	"encoding/json"
+	"net/http"
+	"sql-platform/internal/middleware"
+	"sql-platform/internal/model"
+
+	"github.com/gin-gonic/gin"
+)
+
+// GET /api/v1/user/preferences
+func GetUserPreferences(c *gin.Context) {
+	userID, _, _ := middleware.GetCurrentUser(c)
+	var user model.User
+	if err := model.DB.First(&user, userID).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "User not found"})
+		return
+	}
+
+	prefs := map[string]string{}
+	if user.Preferences != nil && *user.Preferences != "" {
+		json.Unmarshal([]byte(*user.Preferences), &prefs)
+	}
+	c.JSON(http.StatusOK, prefs)
+}
+
+// PUT /api/v1/user/preferences
+func UpdateUserPreferences(c *gin.Context) {
+	userID, _, _ := middleware.GetCurrentUser(c)
+
+	var prefs map[string]string
+	if err := c.ShouldBindJSON(&prefs); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+
+	data, _ := json.Marshal(prefs)
+	str := string(data)
+
+	result := model.DB.Model(&model.User{}).Where("id = ?", userID).Update("preferences", str)
+	if result.Error != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"detail": result.Error.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"message": "Preferences updated", "preferences": prefs})
+}
+
+// GET /api/v1/public/login-style (no auth required)
+func GetPublicLoginStyle(c *gin.Context) {
+	// Check system settings first
+	var setting model.SystemSetting
+	style := "split" // default
+	if model.DB.Where("`key` = ?", "login_style").First(&setting).Error == nil {
+		if setting.Value != "" {
+			style = setting.Value
+		}
+	}
+
+	// Also return theme default
+	theme := "dark"
+	if model.DB.Where("`key` = ?", "default_theme").First(&setting).Error == nil {
+		if setting.Value != "" {
+			theme = setting.Value
+		}
+	}
+
+	c.JSON(http.StatusOK, gin.H{"login_style": style, "theme": theme})
+}

backend/internal/model/model.go

@@ -18,6 +18,7 @@ type User struct {
 	HashedPassword string         `gorm:"size:200;not null" json:"-"`
 	Role           string         `gorm:"size:20;not null" json:"role"` // admin, dba, developer, auditor
 	IsActive       *bool          `gorm:"default:true" json:"is_active"`
+	Preferences    *string        `gorm:"type:text" json:"preferences"` // JSON: {"theme":"dark","login_style":"split"}
 	LastLogin      *time.Time     `json:"last_login"`
 	CreatedAt      time.Time      `gorm:"default:CURRENT_TIMESTAMP" json:"created_at"`
 	UpdatedAt      time.Time      `gorm:"default:CURRENT_TIMESTAMP" json:"updated_at"`