slides: grantable slides.manage permission for non-admin curators

frontend/src/views/AppLayout.vue

@@ -185,8 +185,14 @@ const defaultNav = [
 ]
 
 function buildNavItems(items) {
+  // Drop items the user cannot reach: a nav item may carry a `permission`
+  // (e.g. Slides -> slides.manage); hide it from anyone who lacks it so the
+  // link does not dead-end at the router guard. Admins hold every permission.
+  const visible = items.filter(item =>
+    !item.permission || authStore.hasPermission(item.permission))
+
   // Sort by position
-  const sorted = [...items].sort((a, b) => (a.position || 99) - (b.position || 99))
+  const sorted = [...visible].sort((a, b) => (a.position || 99) - (b.position || 99))
 
   // Assign section headers based on position ranges
   const result = []