refactor: full-stack restructure with multi-tenancy, workspace management, and K8s diagnostics

- Add Workspace domain (entity, repository, service, handler, DTO)
- Add multi-tenant K8s client with tenant binding and quota management
- Add K8s diagnostics client (instance diagnostics)
- Add authorization middleware (authz package)
- Restructure frontend to feature-based architecture (features/)
- Add User Management page in configuration
- Add AccessDenied page and route guards
- Refactor shared components (form inputs, layout, UI)
- Update Tailwind config for new design system
- Add comprehensive documentation (docs/, tasks/, plans)
- Improve cluster service with better kubeconfig handling
- Add tests for crypto, config, helm client, tenant binding

backend/internal/domain/entity/cluster.go

@@ -6,26 +6,31 @@ import (
 
 // Cluster Kubernetes 集群领域实体
 type Cluster struct {
-	ID          string
-	Name        string
-	Host        string    // Kubernetes API Server URL
-	CAData      string    // Base64 encoded CA certificate
-	CertData    string    // Base64 encoded client certificate
-	KeyData     string    // Base64 encoded client key
-	Token       string    // Bearer token (alternative to cert auth)
-	Description string
-	CreatedAt   time.Time
-	UpdatedAt   time.Time
+	ID               string
+	WorkspaceID      string
+	OwnerID          string
+	Visibility       string
+	Name             string
+	Host             string // Kubernetes API Server URL
+	CAData           string // Base64 encoded CA certificate
+	CertData         string // Base64 encoded client certificate
+	KeyData          string // Base64 encoded client key
+	Token            string // Bearer token (alternative to cert auth)
+	Description      string
+	DefaultNamespace string
+	CreatedAt        time.Time
+	UpdatedAt        time.Time
 }
 
 // NewCluster 创建新集群
 func NewCluster(name, host string) *Cluster {
 	now := time.Now()
 	return &Cluster{
-		Name:      name,
-		Host:      host,
-		CreatedAt: now,
-		UpdatedAt: now,
+		Name:       name,
+		Host:       host,
+		Visibility: "private",
+		CreatedAt:  now,
+		UpdatedAt:  now,
 	}
 }
 
@@ -63,6 +68,9 @@ func (c *Cluster) Validate() error {
 	if c.Host == "" {
 		return ErrInvalidClusterHost
 	}
+	if c.Visibility == "" {
+		c.Visibility = "private"
+	}
 	// 必须有认证方式：证书或 Token
 	if (c.CertData == "" || c.KeyData == "") && c.Token == "" {
 		return ErrInvalidClusterAuth
@@ -100,4 +108,3 @@ users:
 
 	return kubeconfig
 }
-