[Vis] Smarter channel presentation order

spinoff from #72 (its parent task)
Default display order of channels is by alphanum channel label.

Investigate : Finding a lightweight application of preset ordering based on groupings of regions: given BIDS electrodes/channel file

Could be in the left side panel, enable skipping by regions.

Start by reading the parent task in issue #72 and locating the existing channel presentation and left-side panel entry points. Review how BIDS electrode or channel files represent regions, then define an agreed ordering and region-skipping behavior; done means the scope and placement are documented clearly enough for implementation.

Written by the indexing model from the issue text.