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/analytics/src/client_tests.rs

@@ -478,6 +478,7 @@ fn sample_thread(thread_id: &str) -> Thread {
         parent_thread_id: None,
         preview: "first prompt".to_string(),
         ephemeral: false,
+        is_pinned: false,
         history_mode: Default::default(),
         model_provider: "openai".to_string(),
         created_at: 1,