Gestion des catégories dans le back-office (admin)

Nouvelle page /backend/categories : lister, ajouter (slug + couleur auto),
renommer et supprimer des catégories. Capacité RBAC manageCategories (admin) ;
lien ajouté à la barre latérale. La suppression détache les adhérents concernés
(transaction) pour éviter toute violation de clé étrangère.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XwfhYHzC9hQWPDnQ2p53GL

src/lib/rbac.ts

@@ -19,10 +19,18 @@ type Capability =
   | "manageMembers"
   | "moderatePromos"
   | "manageAdmins"
+  | "manageCategories"
   | "memberSpace";
 
 const CAPABILITIES: Record<AppRole, Capability[]> = {
-  admin: ["viewDashboard", "manageMembers", "moderatePromos", "manageAdmins", "memberSpace"],
+  admin: [
+    "viewDashboard",
+    "manageMembers",
+    "moderatePromos",
+    "manageAdmins",
+    "manageCategories",
+    "memberSpace",
+  ],
   moderator: ["viewDashboard", "manageMembers", "moderatePromos"],
   editor: ["viewDashboard", "manageMembers"],
   member: ["memberSpace"],