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/style.css

@@ -91,6 +91,11 @@
      be recoloured on its own without dragging every other warning in the app
      with it (Appearance → matrix colours). */
   --mx-cur: var(--warning);
+  /* The "worked with this callsign" dot. Declared ONCE, like --mx-cur: it is
+     drawn over every one of the five cell colours, so it follows the theme's own
+     foreground/background pair rather than a per-theme colour of its own. */
+  --mx-mark-work: var(--foreground);
+  --mx-mark-conf: var(--foreground);
 
   --scrollbar-thumb: #b8a880;
   --scrollbar-thumb-hover: #968455;
@@ -981,6 +986,8 @@
   --color-mx-dx-work: var(--mx-dx-work);
   --color-mx-none: var(--mx-none);
   --color-mx-cur: var(--mx-cur);
+  --color-mx-mark-work: var(--mx-mark-work);
+  --color-mx-mark-conf: var(--mx-mark-conf);
 
   --radius: 0.5rem;