refactor: full-stack restructure with multi-tenancy, workspace management, and K8s diagnostics

- Add Workspace domain (entity, repository, service, handler, DTO)
- Add multi-tenant K8s client with tenant binding and quota management
- Add K8s diagnostics client (instance diagnostics)
- Add authorization middleware (authz package)
- Restructure frontend to feature-based architecture (features/)
- Add User Management page in configuration
- Add AccessDenied page and route guards
- Refactor shared components (form inputs, layout, UI)
- Update Tailwind config for new design system
- Add comprehensive documentation (docs/, tasks/, plans)
- Improve cluster service with better kubeconfig handling
- Add tests for crypto, config, helm client, tenant binding

backend/internal/domain/entity/instance_diagnostics.go

@@ -0,0 +1,70 @@
+package entity
+
+import "time"
+
+type InstanceDiagnostics struct {
+	InstanceName string
+	Namespace    string
+	Pods         []InstancePodDiagnostics
+	Services     []InstanceServiceDiagnostics
+	Events       []InstanceEventDiagnostics
+	Logs         []InstancePodLog
+	CollectedAt  time.Time
+}
+
+type InstancePodDiagnostics struct {
+	Name              string
+	Namespace         string
+	Phase             string
+	NodeName          string
+	PodIP             string
+	HostIP            string
+	RestartCount      int32
+	Containers        []InstanceContainerDiagnostics
+	Conditions        []InstanceConditionDiagnostics
+	CreationTimestamp time.Time
+}
+
+type InstanceContainerDiagnostics struct {
+	Name         string
+	Image        string
+	Ready        bool
+	RestartCount int32
+	State        string
+	Reason       string
+	Message      string
+}
+
+type InstanceConditionDiagnostics struct {
+	Type    string
+	Status  string
+	Reason  string
+	Message string
+}
+
+type InstanceServiceDiagnostics struct {
+	Name      string
+	Namespace string
+	Type      string
+	ClusterIP string
+	Ports     []InstanceEntryPort
+}
+
+type InstanceEventDiagnostics struct {
+	Type           string
+	Reason         string
+	Message        string
+	InvolvedKind   string
+	InvolvedName   string
+	Count          int32
+	FirstTimestamp time.Time
+	LastTimestamp  time.Time
+}
+
+type InstancePodLog struct {
+	Pod       string
+	Container string
+	TailLines int64
+	Log       string
+	Error     string
+}