Add durable per-thread user submission queues (#36952)

## What changed

- Add a storage-neutral `QueueStore` interface backed by a dedicated SQLite
  database for ordered, thread-scoped user submissions.
- Support enqueueing, paginated listing, editing, deletion, and atomic
  reordering, with a limit of 100 pending items per thread.
- Remove queued submissions when their thread is deleted.

## Testing

- Cover concurrent inserts, ordering and pagination, edits, deletion,
  cross-thread isolation, queue limits, and thread cleanup.

GitOrigin-RevId: 0a8e95ac71137afc6f3a039d4b5fc8603110c891

codex-rs/thread-store/src/lib.rs

@@ -8,11 +8,14 @@ mod error;
 mod in_memory;
 mod live_thread;
 mod local;
+mod queue_store;
 mod store;
 mod thread_metadata_sync;
 mod thread_sections;
 mod types;
 
+pub use codex_state::MAX_QUEUE_ITEMS;
+pub use codex_state::QueuedUserSubmissionRecord;
 pub use error::ThreadStoreError;
 pub use error::ThreadStoreResult;
 pub use in_memory::InMemoryThreadStore;
@@ -21,6 +24,8 @@ pub use live_thread::LiveThread;
 pub use live_thread::LiveThreadInitGuard;
 pub use local::LocalThreadStore;
 pub use local::LocalThreadStoreConfig;
+pub use queue_store::LocalQueueStore;
+pub use queue_store::QueueStore;
 pub use store::ThreadStore;
 pub use store::ThreadStoreFuture;
 pub use thread_sections::CreateThreadSectionParams;