Convert tasks, calendar, and dashboard pages from synchronous mock data
to async loading pattern with useState/useEffect. Each page now shows a
loading state via child components while data loads, and displays a
PDA-friendly amber-styled message with a retry button if loading fails.
This prepares these pages for real API integration by establishing the
async data flow pattern. Child components (TaskList, Calendar, dashboard
widgets) already handled isLoading props — now the pages actually use them.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
