fix: add array guards to all frontend components consuming API responses

Prevents "M.forEach is not a function" crashes when API returns error
objects or unexpected shapes instead of arrays. Guards all useQuery
consumers with Array.isArray checks and safe defaults for object props.

Files fixed: DeadlineList, AppointmentList, TenantSwitcher,
DeadlineTrafficLights, UpcomingTimeline, CaseOverviewGrid,
AISummaryCard, TeamSettings, and all page-level components
(dashboard, cases, fristen, termine, ai/extract).

frontend/src/components/settings/TeamSettings.tsx

@@ -118,7 +118,7 @@ export function TeamSettings() {
       </form>
 
       {/* Members List */}
-      {members && members.length > 0 ? (
+      {Array.isArray(members) && members.length > 0 ? (
         <div className="overflow-hidden rounded-md border border-neutral-200">
           {members.map((member, i) => {
             const roleInfo = ROLE_LABELS[member.role] || ROLE_LABELS.member;