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/values_template.go

@@ -0,0 +1,83 @@
+package entity
+
+import (
+	"time"
+)
+
+// ValuesTemplate Values 模板实体（带版本管理）
+type ValuesTemplate struct {
+	ID                string
+	WorkspaceID       string
+	OwnerID           string
+	ChartReferenceID  string
+	Name              string
+	Description       string
+	ValuesYAML        string
+	Version           int      // 模板版本号
+	IsDefault         bool
+	CreatedAt         time.Time
+	UpdatedAt         time.Time
+}
+
+// NewValuesTemplate 创建新 Values 模板
+func NewValuesTemplate(workspaceID, ownerID, chartReferenceID, name, valuesYAML string) *ValuesTemplate {
+	now := time.Now()
+	return &ValuesTemplate{
+		WorkspaceID:      workspaceID,
+		OwnerID:          ownerID,
+		ChartReferenceID: chartReferenceID,
+		Name:             name,
+		ValuesYAML:       valuesYAML,
+		Version:          1,
+		IsDefault:        false,
+		CreatedAt:        now,
+		UpdatedAt:        now,
+	}
+}
+
+// Validate 验证 Values 模板数据
+func (v *ValuesTemplate) Validate() error {
+	if v.Name == "" {
+		return ErrInvalidTemplateName
+	}
+	if v.ValuesYAML == "" {
+		return ErrInvalidTemplateName
+	}
+	return nil
+}
+
+// IncrementVersion 递增版本号
+func (v *ValuesTemplate) IncrementVersion() {
+	v.Version++
+	v.UpdatedAt = time.Now()
+}
+
+// UserConfigOverride 用户配置覆盖实体
+type UserConfigOverride struct {
+	ID          string
+	WorkspaceID string
+	UserID      string
+	TargetType  string // 'storage', 'template', 'global'
+	TargetID    string
+	Config      map[string]interface{}
+	Priority    int
+	IsActive    bool
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+}
+
+// NewUserConfigOverride 创建新用户配置覆盖
+func NewUserConfigOverride(workspaceID, userID, targetType, targetID string, config map[string]interface{}) *UserConfigOverride {
+	now := time.Now()
+	return &UserConfigOverride{
+		WorkspaceID: workspaceID,
+		UserID:      userID,
+		TargetType:  targetType,
+		TargetID:    targetID,
+		Config:      config,
+		Priority:    0,
+		IsActive:    true,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+}