feature: Implement Event stream for Application/Instance/Service  #1472 (#1487)

* Feat: Add event timeline for application/instance/service with K8s event ingestion ([#1472](https://github.com/apache/dubbo-admin/issues/1472))

- Add K8sEvent resource type (proto + Go spec) and store indexes
- Add K8sEventListerWatcher to watch K8s /api/v1/events via client-go
- Register K8sEventListerWatcher in Kubernetes EngineFactory
- Add /application/event, /instance/event, /service/event console API endpoints
- Add EventTimeline shared Vue component with normal/warning node styles
- Wire up event tabs for application, instance, and service detail pages
- Un-hide event tab routes in frontend router
- Add mock event handlers for development
- Add PlatformEvent resource type (platformevent_types.go) with store indexes
- Add shared platform_event_recorder utility for event recording
- Record ZK config change events (tag-route, condition-route, dynamic-config)
- Record ZK metadata events (provider/consumer metadata added/updated)
- Record Nacos instance registration/deregistration events
- Record Nacos consumer metadata change events
- Merge K8s events and Platform events into unified timeline in event query service
- Downgrade "no subscriber" log level from INFO to DEBUG to reduce log noise

* Fix: Address review feedback for K8s event timeline — zero timestamps, watch spam, silent drops, delete-before-add

- K8sEventListerWatcher: check IsZero() before formatting FirstTimestamp/LastTimestamp
  to avoid emitting synthetic "0001-01-01 00:00:00" values that break timeline ordering.
- EventTimeline.vue: remove unconditional watch() that triggered cascading loadMore calls;
  rely solely on IntersectionObserver for scroll-based pagination.
- RecordRegistryEvent: log a warning when dropping events due to empty Mesh or Message
  instead of silently discarding them.
- K8sEventSubscriber.writeEvent: delete the informer-written (original-key) entry only
  after a successful Add of the timestamp-prefixed entry, preventing permanent event
  loss when Add fails.

* Refactor: Rename K8sEvent to LifecycleEvent for unified event model

K8sEvent was originally named for K8s-sourced events only, but now also
carries registry-side events (ZK/Nacos) via the EventSource discriminator.
Rename to LifecycleEvent to accurately reflect its role as a unified
lifecycle event type covering both K8s and registry origins.

- Proto: K8sEvent → LifecycleEvent
- Resource: K8sEventResource → LifecycleEventResource
- Kind: K8sEventKind → LifecycleEventKind
- Subscriber: K8sEventSubscriber → LifecycleEventSubscriber
- Index constants: ByK8sEvent* → ByLifecycleEvent*
- Files: k8s_event.* → lifecycle_event.*
- Retained: K8sEventListerWatcher (K8s-specific component)