Enhance: easier navigation among mailing lists

It's not all that easy to navigate the lists for a large site like the ASF.

There does not appear to be a way to search by list id, and the drop-down lists don't react to typing the first few letters of the name.

No files or tests are named. Start by locating the mailing-list navigation UI and its list-selection controls, then trace how list identifiers and keyboard input are handled. Done means users can find a list by ID and narrow the drop-down by typing the beginning of its name.

Written by the indexing model from the issue text.