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.

Cargo.lock

@@ -5022,7 +5022,6 @@ dependencies = [
  "axum",
  "backon",
  "data-encoding",
- "futures-util",
  "hive-sh4re",
  "reqwest",
  "serde",
@@ -5032,7 +5031,6 @@ dependencies = [
  "thiserror 2.0.18",
  "tokio",
  "tracing",
- "tracing-subscriber",
  "utoipa",
 ]
 
@@ -5062,6 +5060,7 @@ dependencies = [
 name = "swarm-secret-client"
 version = "0.1.0"
 dependencies = [
+ "futures-util",
  "reqwest",
  "rustify",
  "rustify_derive",
@@ -5070,6 +5069,9 @@ dependencies = [
  "serde_json",
  "strum",
  "thiserror 2.0.18",
+ "tokio",
+ "tracing",
+ "tracing-subscriber",
  "vaultrs",
 ]