swarm-controller: read the queue client secret from the store, drop the file

The controller's OIDC client secret (client `swarm-controller`, used for
the queue connection, the auth-bridge bearer and the OTLP push) came from
an operator-placed file, `deploy.swarm-controller.queue.clientSecretFile`,
handed in by `LoadCredential=`.

Now `swarm-secret-publish`, which already copies authelia's minted OIDC
secrets into the store, also publishes this one, to
`swarm/controller/swarm-controller/oidc/client`. That path sits under
`controller/`, which no hive's policy reads. The controller reads it once
at start with its existing store certificate and holds it in memory, as
`swarm_queue_client::ClientSecret::Value`. If the store is down, it
retries for about a minute and then fails the start, so `Restart=` tries
again.

Policy delta: the controller gets `read` on that leaf, and the publisher
gets `create`/`update` on that leaf.

Removed: the `queue.clientSecretFile` option (both spellings, now removed
options with a message), its singleHostSwarm default, the credential and
placeholder, and the path watcher plus its restart oneshot. A controller
without a store identity is now an eval error, because it has no other
way to get the secret.

swarm-logs/src/auth.rs

@@ -24,7 +24,7 @@
 use std::path::{Path, PathBuf};
 
 use anyhow::{Context as _, Result, bail};
-use swarm_queue_client::QueueConfig;
+use swarm_queue_client::{ClientSecret, QueueConfig};
 
 /// Variable prefix for this binary's coordinates.
 ///
@@ -113,7 +113,7 @@ impl Config {
                 url: String::from("unused: swarm-logs mints a token and never connects"),
                 token_endpoint,
                 client_id,
-                client_secret_file: PathBuf::from(client_secret_file),
+                client_secret: ClientSecret::File(PathBuf::from(client_secret_file)),
                 ca_file,
             },
         })