ui: left-hand nav sometimes shows no selection

When clicking around the DB Console, sometimes the left-side nav shows nothing selected.

For instance, when on a table page it shows nothing highlighted: https://localhost:3000/#/table/108

Jira issue: CRDB-68168

Start by reproducing the issue in the DB Console at the table route shown in the report: https://localhost:3000/#/table/108. Trace how the left-hand navigation determines its selected item when moving between pages. Done means the appropriate navigation item remains highlighted on table pages and the behavior is verified while clicking around the console.

Written by the indexing model from the issue text.