fix(ui): light mode visibility + sidebar layout

- Replace accent with primary for upgrade banner (invisible on white bg)
- Fix sidebar actions (theme/logout) stuck at bottom with mt-auto
- Use primary color for user avatar fallback in light mode

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/app/dashboard/DashboardSidebar.tsx

@@ -36,7 +36,8 @@ export function DashboardSidebar() {
       <Separator />
 
       {/* Navigation */}
-      <nav className="flex flex-1 flex-col gap-1 px-3 py-4">
+      <nav className="flex-1 overflow-y-auto px-3 py-4">
+        <div className="flex flex-col gap-1">
           {navItems.map((item) => {
             const isActive = pathname === item.href;
             return (
@@ -55,15 +56,17 @@ export function DashboardSidebar() {
               </Link>
             );
           })}
+        </div>
       </nav>
 
-      <Separator />
+      {/* Bottom section: user + actions */}
-
+      <div className="mt-auto border-t border-border">
         {/* User section */}
         {!isLoading && user && (
+          <>
             <div className="flex items-center gap-2.5 px-4 py-3">
               <Avatar className="size-8 shrink-0">
-            <AvatarFallback className="bg-accent text-accent-foreground text-xs font-semibold">
+                <AvatarFallback className="bg-primary text-primary-foreground text-xs font-semibold">
                   {getInitials(user.name)}
                 </AvatarFallback>
               </Avatar>
@@ -74,16 +77,16 @@ export function DashboardSidebar() {
                   variant="secondary"
                   className={cn(
                     'mt-0.5 w-fit text-xs',
-                user.tier !== 'free' && user.tier && 'border border-accent/20 bg-accent/10 text-accent'
+                    user.tier !== 'free' && user.tier && 'border border-primary/20 bg-primary/10 text-primary'
                   )}
                 >
                   {translateTier(t, user.tier)}
                 </Badge>
               </div>
             </div>
-      )}
-
             <Separator />
+          </>
+        )}
 
         {/* Actions */}
         <div className="px-3 py-3 space-y-1">
@@ -107,6 +110,7 @@ export function DashboardSidebar() {
             </Link>
           </Button>
         </div>
+      </div>
     </aside>
   );
 }

frontend/src/app/dashboard/profile/page.tsx

@@ -421,10 +421,10 @@ export default function ProfilePage() {
                 )}
 
                 {isFreePlan && (
-                  <div className="flex items-center gap-3 p-3 rounded-lg bg-accent/10 border border-accent/20 text-sm">
+                  <div className="flex items-center gap-3 p-3 rounded-lg bg-primary/10 border border-primary/20 text-sm">
-                    <Zap className="w-4 h-4 text-accent flex-shrink-0" />
+                    <Zap className="w-4 h-4 text-primary flex-shrink-0" />
-                    <span className="text-accent/90 flex-1">Débloquez plus de traductions avec un forfait payant.</span>
+                    <span className="text-primary flex-1">Débloquez plus de traductions avec un forfait payant.</span>
-                    <Button asChild size="sm" variant="outline" className="border-accent/30 text-accent hover:bg-accent/10 flex-shrink-0">
+                    <Button asChild size="sm" variant="outline" className="border-primary/30 text-primary hover:bg-primary/10 flex-shrink-0">
                       <Link href="/pricing">Voir les forfaits <ArrowRight className="w-3.5 h-3.5 ml-1" /></Link>
                     </Button>
                   </div>