hive status publishing: read the hive's OIDC secret from the store, retry until it is there

hive-c0re publishes this hive's status to the swarm queue as the OIDC
client `hive-<name>`. Its secret came from
`deploy.hive-controller.statusPublish.clientSecretFile`, which defaulted
to authelia's minted file only on a host running both authelia and the
queue. Every other hive had no secret and never published, so the
controller showed it `never_reported`.

Now `swarm-secret-publish`, beside authelia, also copies each hive's
`hive-<name>` secret to `swarm/hives/<hive>/oidc/client`. Its policy
already allows `swarm/hives/*`. hive-c0re reads that path under the
hive's own store leaf, which the existing `swarm/hives/<hive>/*` grant
covers, and holds the value in memory.

The shared queue client no longer remembers a failed first connect for
the life of the process. A failed attempt is retried with a backoff
from 5s, doubling to a cap of 5 minutes; the dashboard banner stays up
until an attempt succeeds. The two status publishers wait for the
client instead of giving up on the first `None`, so a secret published
after boot is picked up without a restart.

Removed: the `statusPublish.clientSecretFile` option (both spellings,
now removed options with a message), its same-host default, its
LoadCredential, the assertion tying it to the other two coordinates,
and `swarm_queue_client::QueueConfig::from_env`, whose only caller was
this read. Publishing is now on wherever the queue URL and token
endpoint are set and the hive holds a store leaf.

Refs #5015

hive-c0re/src/lifecycle/host_config.rs

@@ -272,8 +272,7 @@ fn queue_agent_credentials(agent_name: &str, dir: Option<&Path>) -> Vec<Credenti
     };
     let secret = dir.join("secret");
     let client_id = dir.join("client_id");
-    // Both or neither, for the same reason `QueueConfig::from_env` refuses a
-    // half-set environment: a client holding one of the two comes up fine and
+    // Both or neither: a client holding one of the two comes up fine and
     // never connects.
     if !secret.is_file() || !client_id.is_file() {
         tracing::info!(