Add persisted thread pinning to the app server (#34840)

## What changed

- Add `isPinned` to thread responses and allow `thread/metadata/update` to pin or unpin stored threads.
- Add an `isPinned` filter to `thread/list`, including cursor-based pagination and combinations with relationship filters.
- Persist pin state in SQLite without modifying rollout files, default existing threads to unpinned, and preserve pins through reconciliation and archive transitions.

## Testing

- Cover protocol serialization, database migration and indexing, pin updates, filtered pagination, rollout reconciliation, and archive/unarchive behavior.

GitOrigin-RevId: c2eacabd6dae465e2ae6ce8a169e00740960cdb7

codex-rs/state/src/extract.rs

@@ -694,6 +694,7 @@ mod tests {
             tokens_used: 1,
             first_user_message: None,
             archived_at: None,
+            is_pinned: false,
             git_sha: None,
             git_branch: None,
             git_origin_url: None,