move agent_token from swarm-queue-client to swarm-agent-verify

per #5471, verifiers stop depending on the queue client. the module is
store-free and needs only thiserror, so swarm-agent-verify gains one
dependency and loses its swarm-queue-client edge. consumers import it
from swarm_agent_verify; swarm-logs and swarm-metrics, whose only use of
swarm-queue-client was this module, drop that dependency, as does
swarm-logs-auth.

hive-subagent-mcp/Cargo.toml

@@ -34,6 +34,8 @@ swarm-queue-client = { workspace = true, features = [
   "agent-inference",
   "agent-permissions",
 ] }
+# The spelling of the token the queue connection presents.
+swarm-agent-verify.workspace = true
 # The agent's own queue credential, read under its store identity.
 swarm-secret-client.workspace = true
 tokio.workspace = true