[Website] Make saved sites sidebar more narrow (#2826)

Changed --site-manager-site-list-width from 320px to 300px to make the
sidebar with saved sites more compact. This improves the #2813
experience.

## Testing Instructions (or ideally a Blueprint)

Go to local Playground confirm the left sidebar is more narrow and yet
still useful

---------

Co-authored-by: Claude <[email protected]>

Author: adamziel

packages/playground/website/src/components/layout/style.module.css

@@ -1,5 +1,5 @@
 :root {
-	--site-manager-site-list-width: 320px;
+	--site-manager-site-list-width: 280px;
 	--site-manager-site-info-min-width: 555px;
 	--site-manager-width-desktop: calc(
 		var(--site-manager-site-list-width) +