fix(colors): Replace hardcoded black with background color token (#5815)

* Update all black to background

* remove --canvas token, keep intentional bg-black

* Move bg-black from grid container to individual viewport panes

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Co-authored-by: Alireza <ar.sedghi@gmail.com>

extensions/tmtv/src/Panels/PanelPetSUV.tsx

@@ -163,7 +163,7 @@ export default function PanelPetSUV() {
   return (
     <>
       <div className="ohif-scrollbar flex min-h-0 flex-auto select-none flex-col justify-between overflow-auto">
-        <div className="flex min-h-0 flex-1 flex-col bg-black text-base">
+        <div className="flex min-h-0 flex-1 flex-col bg-background text-base">
           <PanelSection defaultOpen={true}>
             <PanelSection.Header>{t('Patient Information')}</PanelSection.Header>
             <PanelSection.Content>