fix(ai): warn that upscale and background removal are slow without a GPU (#605)

Add a one-line notice to the upscale and background-removal settings that
heavy AI runs much slower without a GPU and a large image can take minutes,
so a CPU-only self-hoster isn't caught off guard by a slow run. Translated
into all 21 locales.

Refs #591

apps/web/src/components/tools/remove-bg-settings.tsx

@@ -217,6 +217,9 @@ export function RemoveBgControls({ settings, onChange }: RemoveBgControlsProps)
 
   return (
     <div className="space-y-3">
+      <p className="text-xs text-muted-foreground" data-testid="remove-bg-cpu-note">
+        {t.toolSettings["remove-background"].cpuNote}
+      </p>
       {/* Subject type */}
       <SectionLabel>{t.toolSettings["remove-background"].subject}</SectionLabel>
       <div className="grid grid-cols-3 gap-1.5">

apps/web/src/components/tools/upscale-settings.tsx

@@ -70,6 +70,9 @@ export function UpscaleControls({ settings: initialSettings, onChange }: Upscale
 
   return (
     <div className="space-y-4">
+      <p className="text-xs text-muted-foreground" data-testid="upscale-cpu-note">
+        {t.toolSettings.upscale.cpuNote}
+      </p>
       {/* Scale factor */}
       <div>
         <div className="flex justify-between items-center">