refactor: reorganize models to pkg/model and add authentication module

- Move ORM models from internal/model to pkg/model organized by module (auth/k8s/registry)
- Add authentication module with login, user management handlers
- Update all import paths to use new model locations
- Add frontend auth pages (Login, UserManagement) and authStore
- Remove deprecated internal/model/model.go

internal/module/auth/auth.go

@@ -0,0 +1,41 @@
+package auth
+
+import (
+	"context"
+	"log"
+
+	auth "gitea.loveuer.com/loveuer/cluster/pkg/model/auth"
+	"gitea.loveuer.com/loveuer/cluster/pkg/tool"
+	"gorm.io/gorm"
+)
+
+func Init(ctx context.Context, db *gorm.DB) error {
+	if err := db.AutoMigrate(&auth.User{}); err != nil {
+		return err
+	}
+
+	var count int64
+	if err := db.Model(&auth.User{}).Count(&count).Error; err != nil {
+		return err
+	}
+
+	if count == 0 {
+		defaultAdmin := &auth.User{
+			Username:    "admin",
+			Password:    tool.NewPassword("cluster"),
+			Email:       "admin@cluster.local",
+			Nickname:    "Administrator",
+			Role:        "admin",
+			Status:      "active",
+			Permissions: "registry_read,registry_write,cluster_read,cluster_write",
+		}
+
+		if err := db.Create(defaultAdmin).Error; err != nil {
+			return err
+		}
+
+		log.Println("[Auth] Default admin user created: username=admin, password=cluster")
+	}
+
+	return nil
+}