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/quota.go

@@ -0,0 +1,79 @@
+package entity
+
+import (
+	"time"
+)
+
+// ResourceType 资源类型
+type ResourceType string
+
+const (
+	ResourceCPU        ResourceType = "cpu"
+	ResourceGPU        ResourceType = "gpu"
+	ResourceGPUMemory  ResourceType = "gpu_memory"
+)
+
+// WorkspaceQuota 工作空间配额实体
+type WorkspaceQuota struct {
+	ID           string
+	WorkspaceID  string
+	ResourceType ResourceType
+	HardLimit    float64 // 硬限制（0表示无限制）
+	SoftLimit    float64 // 软限制（警告阈值）
+	Used         float64 // 当前使用量
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+// NewWorkspaceQuota 创建新配额
+func NewWorkspaceQuota(workspaceID string, resourceType ResourceType, hardLimit, softLimit float64) *WorkspaceQuota {
+	now := time.Now()
+	return &WorkspaceQuota{
+		WorkspaceID:  workspaceID,
+		ResourceType: resourceType,
+		HardLimit:    hardLimit,
+		SoftLimit:    softLimit,
+		Used:         0,
+		CreatedAt:    now,
+		UpdatedAt:    now,
+	}
+}
+
+// CanAllocate 检查是否可以分配指定资源量
+func (q *WorkspaceQuota) CanAllocate(amount float64) bool {
+	if q.HardLimit == 0 {
+		return true // 无限制
+	}
+	return q.Used+amount <= q.HardLimit
+}
+
+// Allocate 分配资源
+func (q *WorkspaceQuota) Allocate(amount float64) {
+	q.Used += amount
+	q.UpdatedAt = time.Now()
+}
+
+// Release 释放资源
+func (q *WorkspaceQuota) Release(amount float64) {
+	q.Used -= amount
+	if q.Used < 0 {
+		q.Used = 0
+	}
+	q.UpdatedAt = time.Now()
+}
+
+// IsOverLimit 检查是否超过硬限制
+func (q *WorkspaceQuota) IsOverLimit() bool {
+	if q.HardLimit == 0 {
+		return false
+	}
+	return q.Used > q.HardLimit
+}
+
+// IsOverSoftLimit 检查是否超过软限制
+func (q *WorkspaceQuota) IsOverSoftLimit() bool {
+	if q.SoftLimit == 0 {
+		return false
+	}
+	return q.Used > q.SoftLimit
+}