feat: gh-ost真实集成验证通过 + 登录页全面中文化 + 外观设置跨浏览器同步修复

gh-ost集成:
- handler根据instance_id查DB获取连接信息(host/port/user/password)
- 修复gh-ost参数: 去掉不存在的--dry-run(默认noop), 加--execute才真执行
- 加--skip-port-validation(端口映射环境必须)
- 加--allow-on-master(单机MySQL直接执行)
- 加--initially-drop-ghost-table/old-table/socket-file(清理残留)
- GhOstTask增加Port字段, buildArgs同步更新
- dry-run真实验证通过: 连接1.94.55.133:9005, 3行表, 3.85s完成

登录页中文化:
- 5个登录组件(SplitView/CenteredCard/SidePanel/FullImage/MinimalDark)
- 46处英文文案全部替换为中文
- 平台标题统一为'SQL审核平台'

外观设置同步修复:
- GetPublicLoginStyle: GORM First()复用主键导致第二次查询失败
- 改用Take()+重置结构体, 修复theme始终返回dark的bug
- UpdateUserPreferences: 同步写入SystemSetting表(login_style+default_theme)

backend/internal/handler/preferences.go

@@ -43,26 +43,41 @@ func UpdateUserPreferences(c *gin.Context) {
 		c.JSON(http.StatusInternalServerError, gin.H{"detail": result.Error.Error()})
 		return
 	}
+
+	// Sync login_style and theme to SystemSetting so public endpoint picks them up
+	syncToSystemSetting := func(key, value string) {
+		var s model.SystemSetting
+		if model.DB.Where("`key` = ?", key).First(&s).Error == nil {
+			model.DB.Model(&s).Update("value", value)
+		} else {
+			model.DB.Create(&model.SystemSetting{
+				Key: key, Value: value, ValueType: "string",
+				Group: "appearance", Label: key, SortOrder: 0,
+			})
+		}
+	}
+	if v, ok := prefs["login_style"]; ok {
+		syncToSystemSetting("login_style", v)
+	}
+	if v, ok := prefs["theme"]; ok {
+		syncToSystemSetting("default_theme", v)
+	}
+
 	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
+	style := "split"
 	theme := "dark"
-	if model.DB.Where("`key` = ?", "default_theme").First(&setting).Error == nil {
-		if setting.Value != "" {
-			theme = setting.Value
-		}
+
+	var s model.SystemSetting
+	if model.DB.Where("`key` = ?", "login_style").Take(&s).Error == nil && s.Value != "" {
+		style = s.Value
+	}
+	s = model.SystemSetting{} // reset to avoid GORM reusing primary key
+	if model.DB.Where("`key` = ?", "default_theme").Take(&s).Error == nil && s.Value != "" {
+		theme = s.Value
 	}
 
 	c.JSON(http.StatusOK, gin.H{"login_style": style, "theme": theme})