feat: 平台配置全面生效 — 配置策略接入实际逻辑

- query组: ExecuteQuery读取query_limit_max/query_timeout/query_dangerous_pattern
  - 查询超时通过context.WithTimeout生效，db.QueryContext/QueryRowContext
  - 危险模式检测拦截无WHERE的DELETE/UPDATE/DROP/TRUNCATE
  - LIMIT上限从settings读取，不再硬编码1000

- security组: Login读取login_max_attempts/login_lockout_minutes
  - 新增User字段: failed_login_attempts + locked_until
  - 登录失败达到阈值自动锁定，成功时清除计数
  - JWT Token过期时间读取session_timeout_hours设置

- executor组: ExecuteTicket读取executor_timeout/executor_dry_run
  - 执行超时通过context.WithTimeout控制
  - 开启dry_run时先EXPLAIN预检查SQL语法
  - db.ExecContext替代db.Exec

- cleanup组: SettingsCleanupPreview/Run从占位改为真实实现
  - 预览统计4类数据(工单/查询历史/慢日志/审计日志)待清理数量
  - 执行清理按retention_days配置删除过期数据

- ghost组: 13项gh-ost配置加入seedDefaultSettings
  - enabled/path/mode/osc_priority/env/cloud/trigger/chunk/load/lag等
  - 已被ghost.go中getGhostConfig等函数读取

- 前端: PlatformConfigPage新增Ghost/OSC分组显示

backend/internal/handler/instance.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"net/http"
 	"strconv"
+	"strings"
 
 	"sql-platform/internal/middleware"
 	"sql-platform/internal/model"
@@ -66,6 +67,7 @@ func CreateInstance(c *gin.Context) {
 	}
 	// Encrypt password before storing
 	if instance.Password != "" {
+		instance.Password = strings.TrimSpace(instance.Password)
 		encPw, err := encryptPassword(instance.Password)
 		if err == nil {
 			instance.Password = "enc:" + encPw
@@ -75,15 +77,20 @@ func CreateInstance(c *gin.Context) {
 		c.JSON(http.StatusInternalServerError, gin.H{"detail": err.Error()})
 		return
 	}
-	// Auto-detect version and cluster_mode after creation
+	// Auto-detect version, cluster_mode and status after creation
 	go func() {
 		result := testDBConnectionFull(&instance)
 		updates := map[string]interface{}{}
-		if result.Success && result.Version != "" {
-			updates["version"] = result.Version
-		}
-		if result.ClusterMode {
-			updates["cluster_mode"] = true
+		if result.Success {
+			updates["status"] = "connected"
+			if result.Version != "" {
+				updates["version"] = result.Version
+			}
+			if result.ClusterMode {
+				updates["cluster_mode"] = true
+			}
+		} else {
+			updates["status"] = "error"
 		}
 		if len(updates) > 0 {
 			model.DB.Model(&model.Instance{}).Where("id = ?", instance.ID).Updates(updates)
@@ -110,6 +117,7 @@ func UpdateInstance(c *gin.Context) {
 	
 	// if password is empty or masked placeholder, don't update it
 	if pw, ok := input["password"].(string); ok {
+		pw = strings.TrimSpace(pw)
 		if pw == "" || pw == "******" {
 			delete(input, "password")
 		} else {