feat(appearance): give the worked-with-this-call dot its own two colours

The dot is drawn over all five cell backgrounds, so it cannot borrow one of
their colours; it defaults to the theme foreground with a background ring and
now takes two overrides of its own, worked and confirmed, alongside the rest of
the matrix palette.

frontend/src/components/AppearancePanel.tsx

@@ -127,6 +127,12 @@ function MatrixColorsSection() {
             <span className="inline-block w-7 h-5 rounded bg-mx-dx-work" />
             <span className="inline-block w-7 h-5 rounded bg-mx-none" />
             <span className="inline-block w-7 h-5 rounded bg-mx-none ring-2 ring-mx-cur ring-inset" />
+            <span className="relative inline-block w-7 h-5 rounded bg-mx-dx-conf">
+              <span className="absolute top-[4px] right-[4px] size-[5px] rounded-full bg-mx-mark-work ring-1 ring-background" />
+            </span>
+            <span className="relative inline-block w-7 h-5 rounded bg-mx-dx-conf">
+              <span className="absolute top-[4px] right-[4px] size-[5px] rounded-full bg-mx-mark-conf ring-1 ring-background" />
+            </span>
           </div>
 
           <button type="button" onClick={reset}