Frontend api.ts baseUrl is already "/api", so paths like
"/api/cases" produced "/api/api/cases". Stripped the redundant
prefix from all component calls. Rewrite destination correctly
adds /api/ back for the Go backend.
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.