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/storage.go

@@ -0,0 +1,98 @@
+package entity
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// StorageType 存储类型
+type StorageType string
+
+const (
+	StorageTypeNFS     StorageType = "nfs"
+	StorageTypePV      StorageType = "pv"
+	StorageTypeHostPath StorageType = "hostPath"
+)
+
+// StorageConfig 存储配置
+type StorageConfig struct {
+	NFS     *NFSConfig     `json:"nfs,omitempty"`
+	PV      *PVConfig      `json:"pv,omitempty"`
+	HostPath *HostPathConfig `json:"hostPath,omitempty"`
+}
+
+// NFSConfig NFS 配置
+type NFSConfig struct {
+	Server string `json:"server"`
+	Path   string `json:"path"`
+}
+
+// PVConfig PV 配置
+type PVConfig struct {
+	StorageClassName string `json:"storageClassName"`
+	Capacity         string `json:"capacity"`
+	AccessModes      []string `json:"accessModes"`
+}
+
+// HostPathConfig HostPath 配置
+type HostPathConfig struct {
+	Path string `json:"path"`
+}
+
+// StorageBackend 存储后端实体
+type StorageBackend struct {
+	ID          string
+	WorkspaceID string
+	OwnerID     string
+	Name        string
+	Type        StorageType
+	Config      StorageConfig
+	Description string
+	IsDefault   bool
+	IsShared    bool
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+}
+
+// NewStorageBackend 创建新存储后端
+func NewStorageBackend(workspaceID, ownerID, name string, storageType StorageType, config StorageConfig) *StorageBackend {
+	now := time.Now()
+	return &StorageBackend{
+		WorkspaceID: workspaceID,
+		OwnerID:     ownerID,
+		Name:        name,
+		Type:        storageType,
+		Config:      config,
+		IsDefault:   false,
+		IsShared:    false,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+}
+
+// Validate 验证存储后端数据
+func (s *StorageBackend) Validate() error {
+	if s.Name == "" {
+		return ErrInvalidStorageName
+	}
+	if s.Type == "" {
+		return ErrInvalidStorageName
+	}
+	return nil
+}
+
+// ConfigJSON 将配置转为 JSON 字符串
+func (s *StorageBackend) ConfigJSON() (string, error) {
+	data, err := json.Marshal(s.Config)
+	if err != nil {
+		return "", err
+	}
+	return string(data), nil
+}
+
+// ParseConfigJSON 从 JSON 解析配置
+func ParseConfigJSON(jsonStr string) (*StorageConfig, error) {
+	var config StorageConfig
+	err := json.Unmarshal([]byte(jsonStr), &config)
+	return &config, err
+}