Polish Today dashboard loading, errors, and layout (Phase 4).

Add section error boundaries, retry banner with stale-while-revalidate, shared skeletons, responsive action layout, and org-switch refetching.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/today/TodaySectionErrorFallback.tsx

@@ -0,0 +1,13 @@
+import { Card } from '@/components/ui/shared/Card';
+
+interface TodaySectionErrorFallbackProps {
+  message: string;
+}
+
+export function TodaySectionErrorFallback({ message }: TodaySectionErrorFallbackProps) {
+  return (
+    <Card className="min-h-[120px] flex items-center justify-center border-badge-danger-border/40 bg-badge-danger-bg/20">
+      <p className="text-sm text-badge-danger-fg text-center px-4">{message}</p>
+    </Card>
+  );
+}