app-server: expose loaded thread status via read/list and notifications (#11786)

Motivation
- Today, a newly connected client has no direct way to determine the
current runtime status of threads from read/list responses alone.
- This forces clients to infer state from transient events, which can
lead to stale or inconsistent UI when reconnecting or attaching late.

Changes
- Add `status` to `thread/read` responses.
- Add `statuses` to `thread/list` responses.
- Emit `thread/status/changed` notifications with `threadId` and the new
status.
- Track runtime status for all loaded threads and default unknown
threads to `idle`.
- Update protocol/docs/tests/schema fixtures for the revised API.

Testing
- Validated protocol API changes with automated protocol tests and
regenerated schema/type fixtures.
- Validated app-server behavior with unit and integration test suites,
including status transitions and notifications.

codex-rs/app-server/tests/suite/v2/thread_start.rs

@@ -9,6 +9,7 @@ use codex_app_server_protocol::RequestId;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::ThreadStartedNotification;
+use codex_app_server_protocol::ThreadStatus;
 use codex_core::config::set_project_trust_level;
 use codex_protocol::config_types::TrustLevel;
 use codex_protocol::openai_models::ReasoningEffort;
@@ -59,6 +60,7 @@ async fn thread_start_creates_thread_and_emits_started() -> Result<()> {
         thread.created_at > 0,
         "created_at should be a positive UNIX timestamp"
     );
+    assert_eq!(thread.status, ThreadStatus::Idle);
     let thread_path = thread.path.clone().expect("thread path should be present");
     assert!(thread_path.is_absolute(), "thread path should be absolute");
     assert!(