feat(alerts): always-visible dismiss/ack actions + Dismiss all (service, endpoint, UI)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/alerts/use-alerts.ts

@@ -41,6 +41,15 @@ export function useAlertActions() {
   return { acknowledge, dismiss };
 }
 
+export function useDismissAll() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: (filter: { ruleId?: string; severity?: string } = {}) =>
+      apiFetch('/api/v1/alerts/dismiss-all', { method: 'POST', body: filter }),
+    onSuccess: () => queryClient.invalidateQueries({ queryKey: ['alerts'] }),
+  });
+}
+
 export function useAlertRealtime() {
   useRealtimeInvalidation({
     'alert:created': [['alerts']],