Add ThreadManager sample crate (#20141)

Summary:
- Add codex-thread-manager-sample, a one-shot binary that starts a
ThreadManager thread, submits a prompt, and prints the final assistant
output.
- Pass ThreadStore into ThreadManager::new and expose
thread_store_from_config for existing callsites.
- Build the sample Config directly with only --model and prompt inputs.

Verification:
- just fmt
- cargo check -p codex-thread-manager-sample -p codex-app-server -p
codex-mcp-server
- git diff --check

Tests: Not run per request.

codex-rs/Cargo.lock

@@ -3477,6 +3477,27 @@ dependencies = [
  "tempfile",
 ]
 
+[[package]]
+name = "codex-thread-manager-sample"
+version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "codex-arg0",
+ "codex-config",
+ "codex-core",
+ "codex-exec-server",
+ "codex-features",
+ "codex-login",
+ "codex-model-provider-info",
+ "codex-models-manager",
+ "codex-protocol",
+ "codex-rollout",
+ "codex-thread-store",
+ "codex-utils-absolute-path",
+ "tracing",
+]
+
 [[package]]
 name = "codex-thread-store"
 version = "0.0.0"