fix(docs/mobile-sidebar): use opaque sidebar surface instead of 50% white

The drawer aside was set to `bg-white/50 dark:bg-white/[0.01]` with a
`backdrop-blur-3xl`. In light mode this rendered as a 50%-transparent
white panel over the page underneath, which made every item read
"grayed-out" through the blur. In dark mode the 0.01 white was so
faint that the panel was effectively transparent.

Switch to `bg-sidebar` — the opaque sidebar token already used by the
desktop navbar — and drop the backdrop blur (pointless without the
transparency). Items now sit on a solid surface with normal contrast
in both themes.

Author: samjulien

docs/components/layout/mobile-sidebar.tsx

@@ -221,7 +221,7 @@ const MobileSidebar = ({
     >
       <OpenedFoldersProvider>
         <aside
-          className={`flex flex-col w-full max-w-[280px] h-[calc(100vh-8px)] border backdrop-blur-3xl border-r-0 border-border bg-white/50 dark:bg-white/[0.01] rounded-2xl pl-3 pr-1 transition-transform duration-300 ease-out ${
+          className={`flex flex-col w-full max-w-[280px] h-[calc(100vh-8px)] border border-r-0 border-border bg-sidebar rounded-2xl pl-3 pr-1 transition-transform duration-300 ease-out ${
             isVisible ? "translate-x-0" : "translate-x-full"
           }`}
         >