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/app-server-protocol/src/protocol/common.rs

@@ -2725,6 +2725,7 @@ mod tests {
                     parent_thread_id: None,
                     preview: "first prompt".to_string(),
                     ephemeral: true,
+                    is_pinned: false,
                     history_mode: Default::default(),
                     model_provider: "openai".to_string(),
                     created_at: 1,
@@ -2777,6 +2778,7 @@ mod tests {
                         "parentThreadId": null,
                         "preview": "first prompt",
                         "ephemeral": true,
+                        "isPinned": false,
                         "historyMode": "legacy",
                         "modelProvider": "openai",
                         "createdAt": 1,