fix: Guard against undefined members/roles in TeamView

API returns unexpected shape when backend isn't wired — data.members
is undefined, assigned to ref, then .length in template throws
TypeError. Nullish coalescing to empty array prevents the crash.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/admin/TeamView.vue

@@ -27,8 +27,8 @@ async function fetchTeam() {
   isLoading.value = true
   try {
     const data = await api.get<{ members: TeamMember[]; roles: Role[] }>('/team')
-    members.value = data.members
-    roles.value = data.roles
+    members.value = data.members ?? []
+    roles.value = data.roles ?? []
   } catch {
     // API not wired yet
   } finally {