Add persisted manual ordering for thread sections (#36007)

## What changed

- Add `thread/section/move` to atomically move a thread into, within, or out of a section. Threads can be inserted before an existing member or appended, and moves within a section preserve `sectionEnteredAt`.
- Add `section_position` sorting to `thread/list`, with ascending order as its default, and expose `sectionEnteredAt` in thread responses.
- Persist section positions and entry times in SQLite, including migration of existing section members into recency order. Section membership is no longer updated through `thread/metadata/update`.

## Testing

- Cover section moves, reordering, pagination, persistence across restarts and rollout reconciliation, concurrent updates, and rank renumbering.

GitOrigin-RevId: aec6d7ddedca5277029b5caf5c074975397e956c

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

@@ -38,6 +38,7 @@ pub use types::ListItemsParams;
 pub use types::ListThreadsParams;
 pub use types::ListTurnsParams;
 pub use types::LoadThreadHistoryParams;
+pub use types::MoveThreadToSectionParams;
 pub use types::PrepareForkParams;
 pub use types::PreparedFork;
 pub use types::ReadThreadByRolloutPathParams;