fix: 移除initData自动创建默认用户，避免干扰安装流程

initData()启动时自动创建admin/dev/agent默认用户，
导致安装向导提交时checkAdminExists()返回true，返回400系统已安装。
移除自动创建逻辑，管理员由安装向导创建。

backend/internal/database/database.go

@@ -337,59 +337,9 @@ func runMigrations() {
 
 // initData 初始化数据库中的基础数据
 func initData() {
-	hashedPassword, _ := bcrypt.GenerateFromPassword([]byte("123456"), bcrypt.DefaultCost)
-
 	// 修复现有的授权记录，将 is_received 设置为 true
 	DB.Model(&model.AgentApplication{}).Where("is_received = ?", false).Update("is_received", true)
 
-	// 确保管理员用户存在
-	var adminCount int64
-	DB.Model(&model.User{}).Where("username = ?", "admin").Count(&adminCount)
-	if adminCount == 0 {
-		log.Println("Creating admin user...")
-		adminEmail := "admin@example.com"
-		adminUser := model.User{
-			Username: "admin",
-			Email:    &adminEmail,
-			Password: string(hashedPassword),
-			Role:     "admin",
-			Status:   "active",
-		}
-		DB.Create(&adminUser)
-	}
-
-	// 确保开发者用户存在
-	var devCount int64
-	DB.Model(&model.User{}).Where("username = ?", "dev").Count(&devCount)
-	if devCount == 0 {
-		log.Println("Creating dev user...")
-		devEmail := "dev@example.com"
-		devUser := model.User{
-			Username: "dev",
-			Email:    &devEmail,
-			Password: string(hashedPassword),
-			Role:     "admin",
-			Status:   "active",
-		}
-		DB.Create(&devUser)
-	}
-
-	// 确保代理用户存在
-	var agentCount int64
-	DB.Model(&model.User{}).Where("username = ?", "agent").Count(&agentCount)
-	if agentCount == 0 {
-		log.Println("Creating agent user...")
-		agentEmail := "agent@example.com"
-		agentUser := model.User{
-			Username: "agent",
-			Email:    &agentEmail,
-			Password: string(hashedPassword),
-			Role:     "agent",
-			Status:   "active",
-		}
-		DB.Create(&agentUser)
-	}
-
 	// 迁移：将 developer 角色统一为 admin
 	var devRoleCount int64
 	DB.Model(&model.User{}).Where("role = ?", "developer").Count(&devRoleCount)