Add multi-agent runtime metadata types (#25720)

Stack split from #25708. Original PR intentionally left open. This first
PR adds the multi-agent runtime metadata types and catalog plumbing used
by the rest of the stack.

codex-rs/rollout/src/tests.rs

@@ -1274,6 +1274,7 @@ async fn test_updated_at_uses_file_mtime() -> Result<()> {
                 base_instructions: None,
                 dynamic_tools: None,
                 memory_mode: None,
+                multi_agent_version: None,
             },
             git: None,
         }),