drop the shared hive agent login

Every agent now connects to the queue and reads logs with its own secret
from the store (#5181), so the per-hive `hive-<h>-agent` OIDC client has
no reader left. Remove it end to end:

- hive-c0re no longer forwards `hive-queue-agent-{secret,client-id}` into
  containers, and no longer forwards HIVE_AGENT_OIDC_TOKEN_ENDPOINT; the
  agent module that loaded them (nix/agent-modules/queue.nix) is gone, its
  options refused with a removal message.
- The host reader (glue-queue-agent-credential.nix, swarm-bao-queue-agent),
  its store role and policy unit (swarm-bao-queue-agent-policy), its PKI
  leaf and the deploy.bao.queueAgent* / queue.agentCredentialDir options
  are gone; the options are refused with a removal message.
- authelia mints no `hive-<h>-agent` client, and swarm-secret-publish no
  longer writes swarm/hives/<h>/queue/agent.
- swarm-secret-client drops queue::agent_client_path / queue::Credential.
- HIVE_AGENT_NATS_URL is now gated on the agents' queue address alone.

The log store's authelia check stays for operators. swarm-nats-auth still
refuses a `-agent` client id; that refusal and `agentClientSuffix` are left
for a follow-up.

Refs #4459
Refs #4765

nix/module-eval/nats-tls.nix

@@ -77,13 +77,10 @@ let
 
   # The same hive given its own store leaf by hand, which is what turns
   # publishing on away from the IdP's host: hive-c0re reads the status secret
-  # from the store under it. The queue-credential reader's pair comes with it,
-  # because a hive that reads the store is refused at eval without one.
+  # from the store under it.
   hiveLeaf = {
     deploy.bao.clientCertFile = "/etc/pki/h1.pem";
     deploy.bao.clientKeyFile = "/etc/pki/h1-key.pem";
-    deploy.bao.queueAgentClientCertFile = "/etc/pki/h1-queue-agent.pem";
-    deploy.bao.queueAgentClientKeyFile = "/etc/pki/h1-queue-agent-key.pem";
   };
   remotePublishing = hiveWithController (lib.recursiveUpdate remoteSecrets hiveLeaf);