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/errors.go

@@ -5,11 +5,15 @@ import "errors"
 // 领域错误定义
 var (
 	// User errors
-	ErrInvalidUsername = errors.New("invalid username")
-	ErrInvalidPassword = errors.New("invalid password")
-	ErrUserNotFound    = errors.New("user not found")
-	ErrUserExists      = errors.New("user already exists")
-	ErrTokenRevoked    = errors.New("token has been revoked")
+	ErrInvalidUsername    = errors.New("invalid username")
+	ErrInvalidPassword    = errors.New("invalid password")
+	ErrUserNotFound       = errors.New("user not found")
+	ErrUserExists         = errors.New("user already exists")
+	ErrTokenRevoked       = errors.New("token has been revoked")
+	ErrUnauthorized       = errors.New("authentication required")
+	ErrForbidden          = errors.New("permission denied")
+	ErrUserInactive       = errors.New("user is inactive")
+	ErrWorkspaceSuspended = errors.New("workspace is suspended")
 
 	// Cluster errors
 	ErrInvalidClusterName = errors.New("invalid cluster name")
@@ -37,4 +41,8 @@ var (
 	ErrArtifactNotFound     = errors.New("artifact not found")
 	ErrRepositoryNotFound   = errors.New("repository not found")
 	ErrValuesSchemaNotFound = errors.New("values schema not found")
+
+	// Workspace errors
+	ErrWorkspaceNotFound = errors.New("workspace not found")
+	ErrWorkspaceExists   = errors.New("workspace already exists")
 )