Support incremental replay of updated thread items (#35013)

## Why

Persisted item snapshots can be updated after their initial projection while retaining their creation order. Callers need a way to read those updates incrementally without replaying every item.

## What changed

- Track the rollout ordinal of each item's latest snapshot separately from its creation ordinal.
- Let thread-store callers filter items after an exclusive update watermark and sort pages by either creation or update ordinal.
- Keep existing app-server reads creation-ordered, reject incremental reads across forked lineages, and preserve compatibility with older writers.

## Testing

- Cover update-watermark filtering, pagination, sort directions, per-turn reads, cursor validation, forked lineages, migration compatibility, and refreshed item snapshots.

GitOrigin-RevId: d57de849abec27f788e9c384dbff073a0aca1053

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

@@ -31,6 +31,7 @@ pub use types::DeleteThreadsParams;
 pub use types::ExtraConfig;
 pub use types::GitInfoPatch;
 pub use types::ItemPage;
+pub use types::ItemSortKey;
 pub use types::ListItemsParams;
 pub use types::ListThreadsParams;
 pub use types::ListTurnsParams;