feat: add search term to thread list (#12578)

Add `searchTerm` to `thread/list` that will search for a match in the
titles (the condition being `searchTerm` $$\in$$ `title`)

codex-rs/app-server-test-client/src/lib.rs

@@ -916,6 +916,7 @@ fn thread_list(endpoint: &Endpoint, config_overrides: &[String], limit: u32) ->
         source_kinds: None,
         archived: None,
         cwd: None,
+        search_term: None,
     })?;
     println!("< thread/list response: {response:?}");