FR: Kanban board(and stacks) (down) resizing according to markdown viewer font (or own) size (mobile)

The font size used by `YesYouKan` markdown viewer view(`kanban` board UI) doesn't match that of Joplin's settings.

And changing the markdown viewer font size in Joplin's settings doesn't reflect on YesYouKan doing any board size adjustments.

This could be implemented as a user settable plugin setting for font-size and `YesYouKan` would do the resize operations in the background.

**Potential benefits**:

- More cards viewable per stack per screen.
- Less zooming to see stacks side by side and the entire board, by that way having a clearer starting view by default.

Maybe the spacing and padding between cards and stacks could also be reduced to further gain more space?

What do you think of this feature?

Start by locating the YesYouKan markdown viewer and Kanban board UI, then inspect how Joplin's markdown font-size setting is exposed to plugins. Define the responsive board and stack sizing behavior, including any spacing changes, and verify the result on mobile with different font-size settings.

Written by the indexing model from the issue text.