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/ghost.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"fmt"
 	"net/http"
 	"time"
 
@@ -13,15 +14,27 @@ import (
 
 // POST /api/v1/ghost/dry-run
 func GhOstDryRun(c *gin.Context) {
-	var task ghost.GhOstTask
-	if err := c.ShouldBindJSON(&task); err != nil {
+	var req struct {
+		InstanceID int    `json:"instance_id"`
+		Database   string `json:"database"`
+		Table      string `json:"table"`
+		Alter      string `json:"alter"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+
+	// Look up instance connection info
+	task, err := buildGhOstTask(req.InstanceID, req.Database, req.Table, req.Alter)
+	if err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
 		return
 	}
 	task.DryRun = true
 	task.Execute = false
 
-	result, err := ghost.RunGhOst(c.Request.Context(), task, config.C.GhOstPath)
+	result, err := ghost.RunGhOst(c.Request.Context(), *task, config.C.GhOstPath)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, result)
 		return
@@ -29,17 +42,51 @@ func GhOstDryRun(c *gin.Context) {
 	c.JSON(http.StatusOK, result)
 }
 
+// buildGhOstTask resolves instance_id to connection params
+func buildGhOstTask(instanceID int, database, table, alter string) (*ghost.GhOstTask, error) {
+	var inst model.Instance
+	if err := model.DB.First(&inst, instanceID).Error; err != nil {
+		return nil, fmt.Errorf("instance %d not found", instanceID)
+	}
+	if inst.DBType != "mysql" {
+		return nil, fmt.Errorf("gh-ost only supports MySQL instances, got %s", inst.DBType)
+	}
+	// gh-ost needs separate host and port
+	host := inst.Host
+	port := inst.Port
+	return &ghost.GhOstTask{
+		Host:     host,
+		Port:     port,
+		User:     inst.Username,
+		Password: inst.Password,
+		Database: database,
+		Table:    table,
+		Alter:    alter,
+	}, nil
+}
+
 // POST /api/v1/ghost/execute
 func GhOstExecute(c *gin.Context) {
-	var task ghost.GhOstTask
-	if err := c.ShouldBindJSON(&task); err != nil {
+	var req struct {
+		InstanceID int    `json:"instance_id"`
+		Database   string `json:"database"`
+		Table      string `json:"table"`
+		Alter      string `json:"alter"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+
+	task, err := buildGhOstTask(req.InstanceID, req.Database, req.Table, req.Alter)
+	if err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
 		return
 	}
 	task.DryRun = false
 	task.Execute = true
 
-	taskID := ghost.RunGhOstAsync(task, config.C.GhOstPath, nil)
+	taskID := ghost.RunGhOstAsync(*task, config.C.GhOstPath, nil)
 	c.JSON(http.StatusAccepted, gin.H{
 		"task_id": taskID,
 		"message": "gh-ost execution started",