Remove the deprecated thread/rollback API (#44915)

## What changed

Remove `thread/rollback`, its request and response types, generated bindings, and the core `Op::ThreadRollback` operation. Requests now follow the generic unknown-method rejection path. Document `thread/revert` as the alternative for paginated threads.

Keep historical `ThreadRolledBack` markers and legacy error deserialization so existing rollouts remain compatible with replay and migration.

## Testing

Adapt retained-context and Guardian history tests to append legacy rollback markers and resume threads, preserving coverage of surviving instructions, answers, and review history.

GitOrigin-RevId: b3da1becdf86b1869275aacb0ffc2817cee5af2e

codex-rs/app-server/tests/common/test_app_server.rs

@@ -104,7 +104,6 @@ use codex_app_server_protocol::ThreadRealtimeListVoicesParams;
 use codex_app_server_protocol::ThreadRealtimeStartParams;
 use codex_app_server_protocol::ThreadRealtimeStopParams;
 use codex_app_server_protocol::ThreadResumeParams;
-use codex_app_server_protocol::ThreadRollbackParams;
 use codex_app_server_protocol::ThreadSearchOccurrencesParams;
 use codex_app_server_protocol::ThreadSearchParams;
 use codex_app_server_protocol::ThreadSectionMoveParams;
@@ -659,15 +658,6 @@ impl TestAppServer {
         self.send_request("thread/shellCommand", params).await
     }
 
-    /// Send a `thread/rollback` JSON-RPC request.
-    pub async fn send_thread_rollback_request(
-        &mut self,
-        params: ThreadRollbackParams,
-    ) -> anyhow::Result<i64> {
-        let params = Some(serde_json::to_value(params)?);
-        self.send_request("thread/rollback", params).await
-    }
-
     /// Send a `thread/list` JSON-RPC request.
     pub async fn send_thread_list_request(
         &mut self,