feat(frontend): add Helm chart browser, monitoring, chart-references and values templates pages

Add new frontend pages for the multi-tenant OCDP platform:

- Charts page (/charts): Browse Harbor OCI registries to list Helm chart repositories
  and versions, with deploy modal to launch charts on selected clusters
- Monitoring page (/monitoring): Display cluster metrics (CPU/Memory/GPU usage)
  and per-node details with resource utilization bars
- Chart References page (/chart-references): CRUD for chart metadata references
- Values Templates page (/templates): CRUD for Helm values templates with version
  history and rollback support
- Sidebar: Add Charts navigation, update Storage and Templates links
- api.ts: Add all API client functions (clusterApi, registryApi, instanceApi,
  monitoringApi, storageApi, chartReferenceApi, valuesTemplateApi,
  workspaceApi, userApi) with full TypeScript types

Note: deploy flow and values template rollback not yet end-to-end tested.

backend/internal/domain/entity/workspace.go

@@ -0,0 +1,35 @@
+package entity
+
+import (
+	"time"
+)
+
+// Workspace 工作空间实体
+type Workspace struct {
+	ID          string
+	Name        string
+	Description string
+	CreatedBy   string // 创建者用户 ID
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+}
+
+// NewWorkspace 创建新工作空间
+func NewWorkspace(name, description, createdBy string) *Workspace {
+	now := time.Now()
+	return &Workspace{
+		Name:        name,
+		Description: description,
+		CreatedBy:   createdBy,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+}
+
+// Validate 验证工作空间数据
+func (w *Workspace) Validate() error {
+	if w.Name == "" {
+		return ErrInvalidWorkspaceName
+	}
+	return nil
+}