feat: adopt ShadCN chart primitives

Add ChartContainer, ChartConfig, ChartTooltip, ChartTooltipContent
primitives ported from ShadCN's chart pattern. Refactor all 3 chart
locations (dashboard, funnels, uptime) to use CSS variable-driven
theming instead of duplicated CHART_COLORS_LIGHT/DARK objects.

- Add --chart-1 through --chart-5, --chart-grid, --chart-axis CSS vars
- Remove duplicated color objects from 3 files (-223 lines)
- Add accessibilityLayer to all charts
- Rounded bar corners on funnel chart
- Tooltips use Tailwind dark classes instead of imperative style props

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

components/charts/index.ts

@@ -0,0 +1,8 @@
+export {
+  ChartContainer,
+  ChartTooltip,
+  ChartTooltipContent,
+  ChartLegend,
+  ChartLegendContent,
+  type ChartConfig,
+} from './chart'