codex: move unloaded thread writes into store (#18361)

- Migrates unloaded `thread/name/set` and `thread/memoryModeSet`
app-server writes behind the generic
`ThreadStore::update_thread_metadata` API rather than adding one-off
store methods for setting thread name or memory mode.
- Implements the local ThreadStore metadata patch path for thread name
and memory mode, including rollout append, legacy name index updates,
SessionMeta validation/update, SQLite reconciliation, and re-reading the
stored thread.
- Adds focused local thread-store unit coverage plus app-server
integration coverage for the migrated unloaded write paths.

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

@@ -26,7 +26,6 @@ pub use types::LoadThreadHistoryParams;
 pub use types::OptionalStringPatch;
 pub use types::ReadThreadParams;
 pub use types::ResumeThreadRecorderParams;
-pub use types::SetThreadNameParams;
 pub use types::SortDirection;
 pub use types::StoredThread;
 pub use types::StoredThreadHistory;