Refonte UI : design system, logo, shell responsive et pages simples

- Nouveaux tokens (indigo/corail, statuts, plateformes) et mode sombre
- Logo et favicon Social Flow redessinés
- AppShell partagé : sidebar groupée (desktop) + barre de navigation basse (mobile)
- Suppression des pages mobiles dupliquées et des composants morts
- Tableau de bord, connexion, 404, calendrier, médiathèque, IA, statistiques

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017ADkrVcVFTT14hbB148HYS

client/src/hooks/use-session.ts

@@ -0,0 +1,36 @@
+import { useMutation, useQuery } from "@tanstack/react-query";
+import { useLocation } from "wouter";
+import { apiRequest, AUTH_MUTATION, queryClient } from "@/lib/queryClient";
+import { useToast } from "@/hooks/use-toast";
+
+export interface Session {
+  id: string;
+  username: string;
+  role: string;
+}
+
+/** Session courante (mise en cache par react-query, partagée par toute l'app). */
+export function useSession() {
+  const query = useQuery<Session>({
+    queryKey: ["/api/auth/session"],
+    retry: false,
+  });
+  return { ...query, session: query.data, isAdmin: query.data?.role === "admin" };
+}
+
+export function useLogout() {
+  const [, setLocation] = useLocation();
+  const { toast } = useToast();
+  return useMutation({
+    mutationKey: [AUTH_MUTATION, "logout"],
+    mutationFn: async () => {
+      const res = await apiRequest("POST", "/api/auth/logout", {});
+      return await res.json();
+    },
+    onSuccess: () => {
+      queryClient.clear();
+      setLocation("/login");
+      toast({ title: "Déconnecté", description: "À bientôt !" });
+    },
+  });
+}