refactor: update cards to shadcn/ui patterns

- Remove shadow-none border from Card components
- Use var(--chart-1), var(--chart-2) for chart colors
- Add accessibilityLayer to all charts
- Clean up CardHeader/CardContent patterns
- Update CardsStats, CardsActivityGoal, CardsMetric, CardsShare
- Update CardForm base component

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: abdout