archetypes: create an agent from an archetype with no config repo

POST /api/agents takes an archetype the stored list holds, records it in
the new agent-archetype bucket, and queues no CreateRepo, AddRepoMember or
InitAgentConfigRepo for it. A destroy clears the key. Hives may read the
bucket.

Refs #5386

swarm-queue-client/src/lib.rs

@@ -232,6 +232,12 @@ pub mod agent_permissions;
 /// unconditional; writing needs `kv` and reading needs `operator-profiles`.
 pub mod operator_profiles;
 
+/// The bucket swarm-controller records each archetype agent's archetype in
+/// — one key per agent, read by the hive that runs it. The names and the
+/// stored type are unconditional; writing needs `kv` and reading needs
+/// `agent-archetype`.
+pub mod agent_archetype;
+
 /// The login flag in an agent's turn-state header. No bucket: it travels
 /// on [`agent_state_subject`] only.
 pub mod agent_login;