v1.4.21

feat: v1.4.21 — node-only macula_mesh_client (P1 refactor)

Strips the relay role from the SDK. The mesh_client sends
type=<<"node">> in CONNECT, full stop. Peer role moves to a dedicated
macula_peer_client module in the macula-relay repo with its own
supervisor, its own subsystem folder, and its own lifecycle owner
(peering).

- type option + client_type state field removed
- async_call/7 removed (peer-only path)
- _swim.* PUBLISH handler + route_swim helpers removed (dead code
  for nodes: relays only send SWIM on peer connections)
- unwrap_reply helper removed (only used by async_call path)

Invariants that used to be enforced by runtime guards
({identified, is_peer}) now live in module boundaries. The SDK is
incapable of identifying as a relay.

No runtime consumer affected — the only caller of type=<<"relay">>
was macula-relay, which migrates in a matching commit.

P1 of the relay refactor plan (see macula-relay/plans/
PLAN_MACULA_RELAY_REFACTOR.md).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>