feat(core): K8s Endpoints API watcher for ServiceMap

[crrow]

Context

MetaService design (docs/design/meta-service.md lines 70-85) requires watching K8s Endpoints API for live topology awareness. Currently using StaticServiceMap placeholder.

Acceptance Criteria

• Implement K8sServiceMap that implements the ServiceMap trait
• Watch K8s Endpoints API for Ingestor and Streamer services
• Map internal pod IPs to externally reachable node_ip:node_port pairs
• Update service map immediately on topology changes (scale up/down, pod failure)
• Feature-gated behind k8s cargo feature flag

Dependencies

• ServiceMap trait (to be added in metaservice alignment work)