refactor backend packages and global db service

backend/internal/models/user.go

@@ -0,0 +1,17 @@
+package models
+
+import "time"
+
+type SenlinAgentUser struct {
+	ID           uint   `gorm:"primaryKey"`
+	Email        string `gorm:"uniqueIndex;not null"`
+	DisplayName  string `gorm:"not null"`
+	PasswordHash string `gorm:"not null"`
+	Role         string `gorm:"not null;default:user"`
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+func (SenlinAgentUser) TableName() string {
+	return "senlin_agent_users"
+}