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/chart_reference.go

@@ -0,0 +1,41 @@
+package entity
+
+import (
+	"time"
+)
+
+// ChartReference Chart 引用实体
+type ChartReference struct {
+	ID           string
+	WorkspaceID  string
+	RegistryID   string
+	Repository   string
+	ChartName    string
+	Description  string
+	IsEnabled    bool
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+// NewChartReference 创建新 Chart 引用
+func NewChartReference(workspaceID, registryID, repository, chartName, description string) *ChartReference {
+	now := time.Now()
+	return &ChartReference{
+		WorkspaceID: workspaceID,
+		RegistryID:  registryID,
+		Repository:  repository,
+		ChartName:   chartName,
+		Description: description,
+		IsEnabled:   true,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+}
+
+// Validate 验证 Chart 引用数据
+func (c *ChartReference) Validate() error {
+	if c.Repository == "" {
+		return ErrInvalidChart
+	}
+	return nil
+}