Cover area scaleability design

## Scope

@ Design

- [ ] Define the rules of how images are displayed on diff screen sizes

@ Dev
>goes to community dev pipe
- [ ] Implement the designed solution (show diff images for diff screen sizes)

## Context

The cover area for both the landing screen and the channels needs to be re-evaluated with a strategy for how to be responsive, and what requirements to have for the imagery. Currently we are doing an ad-hoc approach which mixes things from the design and ideas that have been introduced later.

Begin with the cover areas on the landing screen and channels, and define rules for displaying images across different screen sizes, including imagery requirements. The design is done when the responsive strategy is documented; implementation is complete when diff images display appropriately at the target screen sizes through the community dev pipe.

Written by the indexing model from the issue text.