refactor(swarm-queue-client): share the hive-status bucket's name and shape

The bucket has two ends in two crates: a hive writes its own key, the
controller reads every key. `swarm-controller` declared the name as a
private const with a doc comment arguing that "reader and writer must
name the same bucket" — an argument the writer, in another crate, could
not obey.

The name is the mild half. Both ends do get-or-create, because either may
come up first on a fresh swarm and neither can assume the other has run.
Two `Config`s that drift means whichever end created the bucket wins and
the other's `get_key_value` succeeds against a bucket it did not ask for:
no error, no log, just a retention policy nobody chose. Sharing the
constructor gives that race one outcome.

Behind a default-off `kv` feature, so the crate's other consumer — the
auth-callout responder, which speaks the connect and nothing else — still
pulls neither `jetstream` nor `kv`. That was the actual reason the
feature was excluded when this crate was extracted; the flag preserves
it. The surface is deliberately narrow: one bucket's name and creation
config, not a general KV facade.

swarm-queue-client/src/lib.rs

@@ -112,6 +112,12 @@ pub fn chain(error: &dyn std::error::Error) -> String {
     rendered
 }
 
+/// The hive-status KV bucket, shared by the hive that writes it and the
+/// controller that reads it. Behind the `kv` feature — see the module doc
+/// for why a bucket name and its config belong to neither end alone.
+#[cfg(feature = "kv")]
+pub mod status;
+
 /// Only the one field this needs; authelia returns several.
 #[derive(serde::Deserialize)]
 struct TokenResponse {