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).
Backend: PUT /api/tenants/{id}/settings endpoint for updating tenant
settings (JSONB merge). Frontend: /einstellungen page with CalDAV
config (URL, credentials, calendar path, sync toggle, interval),
manual sync button, live sync status display. /einstellungen/team
page with member list, invite-by-email, role management.
