feat(ui-polish): sidebar icons + topbar + dashboard redesign

- Sidebar: lucide-react icons, lock on gated items, upgrade badge on "Mon plan", user footer with avatar initials + plan label, "EX|PRIA" logo header
- Topbar: sticky with backdrop-blur, breadcrumb via centralized route-titles.ts, search placeholder, keyboard shortcuts + notifications icons
- Dashboard: split into Free/Standard/Premium views (ARCHITECTURE.md §3 aligned)
- NclcHero: NCLC display + gauge 5→10 + SVG score ring
- StatCards: simulations remaining + NCLC estimé + dernier score with delta
- RecentSimulations: 3 latest with NCLC badge + chevron nav
- NextStepCard: static recommendation per plan
- PaywallBanner: full-width redesign + fixed dead Boréal tokens
- Removed orphan MobileHeader.tsx (0 consumers)

Typecheck: OK · Tests: 122/122 ✅

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/AppLayout.tsx

@@ -1,20 +1,20 @@
 /**
  * Layout applicatif — enveloppe toutes les routes privées.
  *
- * Desktop (≥ 1024px) : Sidebar fixe 240px + zone contenu principale.
- * Mobile (< 1024px)  : MobileHeader sticky + drawer slide-in + BottomNav fixe.
+ * Desktop (≥ 1024px) : Sidebar fixe 230px + Topbar sticky + zone contenu.
+ * Mobile (< 1024px)  : Topbar avec hamburger + drawer slide-in + BottomNav fixe.
  *
  * Le drawer mobile se ferme automatiquement à chaque changement de route
  * (useEffect sur location.pathname).
  *
- * Règle L : tokens Direction H exclusivement.
+ * Règle L : tokens du design system exclusivement.
  * Règle H : aucune logique métier — plan lu depuis le cache TanStack Query.
  */
 
 import { useState, useEffect } from 'react'
 import { useLocation } from 'react-router-dom'
 import { Sidebar } from './Sidebar'
-import { MobileHeader } from './MobileHeader'
+import { Topbar } from './Topbar'
 import { BottomNav } from './BottomNav'
 import { usePlan } from '@/features/dashboard/hooks/usePlan'
 import { cn } from '@/shared/lib/utils'
@@ -31,8 +31,6 @@ export function AppLayout({ children }: AppLayoutProps) {
   const plan: Plan = data?.plan ?? 'free'
 
   // Ferme le drawer à chaque changement de route.
-  // Synchronisation UI → router state : pattern légitime (source externe = React
-  // Router). Bail-out React si déjà fermé = zéro cascading render en pratique.
   useEffect(() => {
     // eslint-disable-next-line react-hooks/set-state-in-effect
     setIsMobileMenuOpen(false)
@@ -51,9 +49,6 @@ export function AppLayout({ children }: AppLayoutProps) {
         <Sidebar plan={plan} />
       </aside>
 
-      {/* ── MOBILE — Header sticky ─────────────────────────────────── */}
-      <MobileHeader onMenuOpen={() => setIsMobileMenuOpen(true)} />
-
       {/* ── MOBILE — Drawer overlay ────────────────────────────────── */}
       <div
         aria-hidden="true"
@@ -81,6 +76,7 @@ export function AppLayout({ children }: AppLayoutProps) {
         className="min-h-screen pb-16 lg:pb-0 lg:pl-[230px]"
         style={{ background: mainBackground }}
       >
+        <Topbar onMobileMenuOpen={() => setIsMobileMenuOpen(true)} />
         <div className="mx-auto max-w-[1100px] px-5 py-6 lg:px-9 lg:py-9">{children}</div>
       </main>