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/v2/thread.rs

@@ -865,6 +865,9 @@ pub struct ThreadMetadataUpdateParams {
     /// provide a string to replace the stored value.
     #[ts(optional = nullable)]
     pub git_info: Option<ThreadMetadataGitInfoUpdateParams>,
+    /// Patch whether this thread is pinned. Omit to leave the stored value unchanged.
+    #[ts(optional = nullable)]
+    pub is_pinned: Option<bool>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -1118,6 +1121,9 @@ pub struct ThreadListParams {
     /// If false or null, only non-archived threads are returned.
     #[ts(optional = nullable)]
     pub archived: Option<bool>,
+    /// Optional pinned filter; when set, only threads matching this value are returned.
+    #[ts(optional = nullable)]
+    pub is_pinned: Option<bool>,
     /// Optional cwd filter or filters; when set, only threads whose session cwd
     /// exactly matches one of these paths are returned.
     #[ts(optional = nullable, type = "string | Array<string> | null")]