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/messages/en.json

@@ -216,7 +216,10 @@
     "upcomingAppointmentsTitle": "Upcoming Today",
     "upcomingAppointmentsSubtitle": "Appointments not yet finished",
     "viewAllAppointments": "View schedule",
-    "noUpcomingAppointments": "No upcoming appointments for the rest of today."
+    "noUpcomingAppointments": "No upcoming appointments for the rest of today.",
+    "retryLoad": "Try again",
+    "sectionLoadError": "This section could not be displayed.",
+    "lastUpdated": "Updated at {time}"
   },
   "staff": {
     "redirecting": "Redirecting…",