move stored_secret from swarm-queue-client to swarm-secret-client

The module is a rename (97% similar); everything else in the diff follows
from the move:

- stored_secret.rs: private `chain()` helper, the 8-line copy of the queue
  crate's `chain` the module called as `crate::chain`; the queue crate's
  public `chain` stays.
- stored_secret.rs: `Duration::from_mins(5)` in `MAX_REREAD_DELAY` is
  unchanged moved code, not a new use.
- swarm-secret-client Cargo.toml: gains futures-util, tokio and tracing as
  dependencies and tokio `test-util` plus tracing-subscriber as dev
  dependencies; the module and its tests use them.
- swarm-queue-client Cargo.toml: drops futures-util and the tracing-subscriber
  dev dependency, which only the moved module used; its tokio dev comment is
  reworded to the tests that remain.
- Cargo.lock: the same dependency moves, nothing else.
- swarm-queue-client lib.rs: imports `swarm_secret_client::stored_secret`,
  and its tests use a small local `Store` in place of the moved module's
  test-only `Fake`, which is no longer reachable.
- callers (hive-c0re, swarm-builder, swarm-ci-metrics, swarm-claude-login,
  swarm-controller, swarm-nats-auth, swarm-review-classifier): import path
  only; no re-export is left behind.

swarm-controller/src/forge.rs

@@ -42,7 +42,7 @@ use utoipa::ToSchema;
 
 use crate::webhook::DeliveryKind;
 use swarm_queue_client::review_classifier::Commit;
-use swarm_queue_client::stored_secret::StoredSecret;
+use swarm_secret_client::stored_secret::StoredSecret;
 
 pub mod agent_token;
 mod api;