v0.0.5: Add output aspect ratio (16:9, 4:3, 1:1) with fit or fill

A phone held upright produces portrait video. The receiver can now reframe
it natively (bilinear, parallel) into a landscape frame that keeps the
source's short side, e.g. 1080x1920 -> 1920x1080, either padded with black
bars (fit) or center-cropped (fill). Applies to the preview, snapshots and
the virtual camera; the choice is saved.