Selecting a pending disc in the PS1 tab now shows a live preview of the
ICON0 (144x80 XMB icon) and PIC1 (480x272 launch background) that the
converter would embed, fetched asynchronously so the UI stays responsive.
Converted discs/EBOOTs show an 'already converted' notice, and ps1_art now
falls back to a name-derived cache key when a disc has no serial.
Fetch the game's cover art (libretro / ScreenScraper / IGDB / Wikipedia,
reusing the local cover cache) and bake it into the EBOOT's ICON0 (144x80
XMB icon) and PIC1 (480x272 launch background) instead of the default PS1
icon. Best-effort: falls back to the base icon/empty background when no art
is found. convert()/convert_to_folder() gain optional icon0/pic1 params.
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