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/src/charts/index.ts

@@ -0,0 +1,20 @@
+// Charts - Statistics Visualization Components
+export { default as StatsGrid } from './StatsGrid.svelte';
+export { default as ActivityHeatmap } from './ActivityHeatmap.svelte';
+export { default as TrendLineChart } from './TrendLineChart.svelte';
+export { default as DonutChart } from './DonutChart.svelte';
+export { default as ProgressBars } from './ProgressBars.svelte';
+export { default as StatisticsSkeleton } from './StatisticsSkeleton.svelte';
+
+// Types
+export type {
+	StatVariant,
+	StatItem,
+	HeatmapDataPoint,
+	TrendDataPoint,
+	DonutSegment,
+	ProgressItem,
+} from './types';
+
+// Constants
+export { STAT_VARIANT_COLORS } from './types';