fix(sidebar): largeur responsive plus fiable (seuil md au lieu de xl)

La sidebar restait à 320px en production car l'élargissement ne se
déclenchait qu'à partir du breakpoint xl (1280px). Abaisse le seuil à
md (768px) pour couvrir tous les écrans desktop en production.

- < 768px (mobile, overlay) : w-80 (320px)
- >= 768px : w-[22rem] (352px)
- >= 1536px : w-[26rem] (416px)

Le fallback Suspense du layout est aligné pour éviter tout décalage.

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/app/(main)/layout.tsx

@@ -37,7 +37,7 @@ export default async function MainLayout({
     >
       {/* No top-bar header — sidebar-only navigation (architectural-grid design) */}
       <div className="flex h-screen overflow-hidden bg-memento-desk dark:bg-background">
-        <Suspense fallback={<div className="hidden w-80 xl:w-[22rem] 2xl:w-[26rem] shrink-0 md:block h-full self-stretch" />}>
+        <Suspense fallback={<div className="hidden w-80 md:w-[22rem] 2xl:w-[26rem] shrink-0 md:block h-full self-stretch" />}>
           <Sidebar user={session?.user} />
         </Suspense>
 

memento-note/components/sidebar.tsx

@@ -1182,7 +1182,7 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
           isImmersiveRoute && userCollapsed
             ? 'fixed inset-y-0 start-0 z-[70]'
             : 'fixed inset-y-0 start-0 z-[70] md:relative md:z-auto',
-          'h-full min-h-0 w-80 xl:w-[22rem] 2xl:w-[26rem] shrink-0 flex flex-row overflow-hidden self-stretch',
+          'h-full min-h-0 w-80 md:w-[22rem] 2xl:w-[26rem] shrink-0 flex flex-row overflow-hidden self-stretch',
           'transition-transform duration-300 ease-in-out',
           isImmersiveRoute && userCollapsed
             ? '-translate-x-full'