feat: responsive widgets, atemschutz permission UX, event hard-delete

- fix dashboard grid: use auto-fill instead of auto-fit for equal-width widgets
- atemschutz: skip stats/members API calls for non-privileged users, hide
  empty Aktionen column, add personal status subtitle
- kalender: add permanent delete option for events with confirmation dialog

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

frontend/src/pages/Dashboard.tsx

@@ -33,7 +33,7 @@ function Dashboard() {
         <Box
           sx={{
             display: 'grid',
-            gridTemplateColumns: 'repeat(auto-fit, minmax(280px, 1fr))',
+            gridTemplateColumns: 'repeat(auto-fill, minmax(280px, 1fr))',
             gap: 2.5,
             alignItems: 'start',
           }}