Double click track panel to add new mono audio track

### Problem to be solved

A lot of DAWs (such as reaper) support double clicking the track list to quickly add a new track. It's a helpful QOL feature.

### Your idea

Double left clicking anywhere within the Click Area would add a new mono track. I figure a mono track is much more common to add than a stereo or label so it makes sense for that to be the default.

Maybe right clicking in the area would open the standard 'add track' options (mono, stereo, label), or a context menu containing those options.

### Prior art

Double clicking the track area in Reaper adds a new track.

### Additional context

_No response_

Start by locating the track panel and its Click Area implementation, then trace the existing add-track actions and track creation code. The work is done when double left clicking the area creates a mono track and the existing mono, stereo, and label options continue to work unchanged.

Written by the indexing model from the issue text.