feat(shared-ui): add unified statistics components with theme support

- Add reusable chart components in shared-ui (StatsGrid, ActivityHeatmap, TrendLineChart, DonutChart, ProgressBars, StatisticsSkeleton)
- Use CSS variables (--primary) for consistent theme-based styling
- Add statistics pages to Calendar and Contacts apps
- Add statistics stores with app-specific metrics
- Fix PriorityDonutChart layout in Todo app (vertical layout with 2x2 legend grid)
- Add date-fns dependency to shared-ui

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/shared-ui/package.json

@@ -42,6 +42,7 @@
 		"d3-selection": "^3.0.0",
 		"d3-transition": "^3.0.0",
 		"d3-zoom": "^3.0.0",
+		"date-fns": "^4.1.0",
 		"lucide-svelte": "^0.468.0"
 	},
 	"devDependencies": {