feat: quest page frontend — accept, progress, claim, arcs narratifs

Nouvelle page /quests avec icône Scroll dans la sidebar.
Layout: quêtes actives (gauche) + disponibles (droite) + arcs en bas.
Progress bars, boutons accepter/réclamer, badges répétable.
Arc section collapsible avec status par quête.

frontend/src/components/Layout.tsx

@@ -1,9 +1,10 @@
 import { Link, useLocation } from 'react-router-dom';
 import { useAuth } from '../context/AuthContext';
-import { Swords, Package, Hammer, User, LogOut, Shield } from 'lucide-react';
+import { Swords, Package, Hammer, User, LogOut, Shield, Scroll } from 'lucide-react';
 
 const NAV = [
   { to: '/dashboard', icon: User,    label: 'Personnage' },
+  { to: '/quests',    icon: Scroll,  label: 'Quêtes' },
   { to: '/combat',    icon: Swords,  label: 'Combat' },
   { to: '/inventory', icon: Package, label: 'Inventaire' },
   { to: '/craft',     icon: Hammer,  label: 'Artisanat' },