p2p: implement worker registration/heartbeats + discovery per spec (DHT queue/pool) #199
Description
Goal
Replace static validator_worker_ids bootstrapping with spec-aligned worker registration, heartbeat, and selection/discovery.
Scope
- WorkerRecord schema and persistence
- Registration/heartbeat messages
- Selection rules and stale removal
- Region/latency considerations if required by spec
Acceptance criteria
- A node can join, register, and be selected without manual config lists
- Stale workers are pruned
- Tests simulate churn and partitions