style(app): remove border radius on commit-body

Removes the rounded corners on the commit-body by setting border-radius to 0.
This makes the component use a flat edge and aligns with the design system.

- Remove dependency on ui radius variable for commit-body

src/app.css

@@ -6080,7 +6080,7 @@ input:focus, textarea:focus, select:focus { box-shadow: 0 0 0 3px color-mix(in s
 .graph-list { background: var(--color-surface-solid); }
 .graph-gutter { background: var(--color-surface-dim); }
 .commit-body {
-  border-radius: var(--ui-radius-sm);
+  border-radius: 0;
   background: color-mix(in srgb, var(--color-primary) 7%, var(--color-surface-solid));
   box-shadow: none;
 }