The home background PNGs shipped since #7280 total ~67 MB and bloat
every clone and pull for other devs. Encode them as JPEG at quality 95
(matching resolution, visually lossless at 40-48 dB PSNR since the art
is noise-heavy renders PNG cannot compress) for ~79% size reduction.
The scheme-variant and theme asset resolution already probe .jpg, so
only the qrc entries needed updating.
Refs #7327
Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
