feat(storage): route raft from cluster metadata

[Aetherance]

Part 4 of the membership stack.

Depends on #3.

Summary

• resolve Raft destinations from the replicated cluster metadata registry
• refresh transport routes after membership changes, address updates, and snapshots
• carry and validate cluster identity in Raft envelopes
• report snapshot delivery failures and guard against stale address updates

Review scope

This PR connects committed membership to transport routing. The public cluster API is handled by the next PR.