feat(frontend): convertit l'ensemble des pages et composants au DSFR

- composants UI (Input, Card, Badge, Modal, ConfirmDialog, Slider, Skeleton,
  ThemeToggle) + Sidebar
- pages auth (connexion, inscription)
- pages publiques (informations, détail, contacts urgence, mentions, RGPD)
- espace membre (dashboard, journal, wizard saisie via fr-stepper, rapports, profil)
  + composants tracker (EditSaisieModal, EmotionPicker, TrackerTimeline, EmotionChart)
- back-office admin (dashboard, utilisateurs, contenus, émotions)

Suppression de Tailwind candlelight/malachite + lucide-react. Build OK (20 routes).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/app/(auth)/layout.tsx

@@ -0,0 +1,13 @@
+export default function AuthLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return (
+    <div className="fr-container fr-py-8w">
+      <div className="fr-grid-row fr-grid-row--center">
+        <div className="fr-col-12 fr-col-md-8 fr-col-lg-6">{children}</div>
+      </div>
+    </div>
+  );
+}