Need a "no filter" button and/or toggle-state filtering buttons

In the thumbview, there is no obvious mechanism to clear all filters. Currently tied to the 'R' key.

One idea is to have the tagged/untagged/filter buttons all be "toggle" buttons, where un-toggling them would be a clear. Possibly confusing given (e.g.) that clicking 'untagged' would un-do a 'tagged' toggle AND un-do a 'filter' toggle.

Start at the thumbview's existing filter controls and the R-key reset path. Decide whether to use a dedicated no-filter control or toggle-state behavior, then make the chosen interaction clear all active filters and verify the tagged, untagged, and filter states.

Written by the indexing model from the issue text.