style: replace raw colors.css refs with glass tokens from constant.css

Replace @foreground, @primary, @error, @outline, @shadow, @secondary
and their var() equivalents with semantic glass-* tokens across 22 files.
Colors without glass equivalents (@on-primary, @cyan, etc.) left as-is.

src/styles/widgets/dropdown.css

@@ -33,7 +33,7 @@
 #dropdown-option-label {
   font-size: apply(font-md);
   margin: 0px;
-  color: @foreground;
+  color: @glass-text;
   font-weight: 400;
 }