Fetch and display a line chart of confirmed cases over time for selected country.
Acceptance Criteria:
- Fetch /dayone/country/{slug}.
- Loading state while fetching.
- Cumulative confirmed over time line.
- Abort or guard against stale updates on country change.
- Placeholder swapped for chart component.
Files: src/pages/Covid.jsx, new src/components/CountryTrendChart.jsx
Fetch and display a line chart of confirmed cases over time for selected country.
Acceptance Criteria:
Files: src/pages/Covid.jsx, new src/components/CountryTrendChart.jsx