fix(styles): show graph hover branches only on gutter hover

Hover behavior for graph branch highlights was adjusted to limit the
opacity/transform changes to the gutter hover state. This prevents the
highlight from triggering when hovering over the graph rows, reducing
unintended visual effects.

src/app.css

@@ -2223,8 +2223,7 @@
     transform: translateY(-50%) translateX(-4px);
     transition: opacity 120ms ease, transform 120ms ease;
   }
-  .graph-gutter:hover .graph-hover-branches,
-  .graph-row:hover .graph-hover-branches {
+  .graph-gutter:hover .graph-hover-branches {
     opacity: 1;
     transform: translateY(-50%) translateX(0);
   }