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/window/battery.css

@@ -89,7 +89,7 @@
 }
 .battery-settings-button label {
   font-weight: 500;
-  color: @foreground;
+  color: @glass-text;
 }
 #energy-mode-button:first-child {
   margin-top: 0;