feat: MySQL/PG 实时指标采集 + 版本检测修复 + 密码加密存储

- 新增 getMySQLMetrics(): SHOW GLOBAL STATUS 采集连接数/QPS/延迟/运行时间
- 新增 getPostgresMetrics(): pg_stat_activity 采集活跃连接+运行时间
- 修复 extractVersion(): 支持 Redis 'version: 7.4.9, mode: standalone' 格式(逗号截断)
- CreateInstance/UpdateInstance: 创建/更新时自动加密密码(enc: 前缀)
- InstanceMetrics handler: MySQL/PG 分别调用专属 metrics 函数

backend/internal/handler/instance.go

@@ -64,6 +64,13 @@ func CreateInstance(c *gin.Context) {
 		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
 		return
 	}
+	// Encrypt password before storing
+	if instance.Password != "" {
+		encPw, err := encryptPassword(instance.Password)
+		if err == nil {
+			instance.Password = "enc:" + encPw
+		}
+	}
 	if err := model.DB.Create(&instance).Error; err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"detail": err.Error()})
 		return
@@ -105,6 +112,13 @@ func UpdateInstance(c *gin.Context) {
 	if pw, ok := input["password"].(string); ok && pw == "******" {
 		delete(input, "password")
 	}
+	// Encrypt password if provided and not masked
+	if pw, ok := input["password"].(string); ok && pw != "" {
+		encPw, err := encryptPassword(pw)
+		if err == nil {
+			input["password"] = "enc:" + encPw
+		}
+	}
 	
 	if err := model.DB.Model(&instance).Updates(input).Error; err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"detail": err.Error()})
@@ -191,8 +205,13 @@ func InstanceMetrics(c *gin.Context) {
 	case "redis":
 		metrics := getRedisMetrics(&instance)
 		c.JSON(http.StatusOK, metrics)
+	case "mysql":
+		metrics := getMySQLMetrics(&instance)
+		c.JSON(http.StatusOK, metrics)
+	case "postgresql", "postgres", "pg":
+		metrics := getPostgresMetrics(&instance)
+		c.JSON(http.StatusOK, metrics)
 	default:
-		// For MySQL/PG: return basic status
 		c.JSON(http.StatusOK, gin.H{
 			"status":  "online",
 			"version": instance.Version,