Replace fontsource with next/font/google and update react-zen.

- Switch from @fontsource/inter to next/font/google for font loading
- Update @umami/react-zen to v0.229.0
- Add type augmentation for react-zen missing children props
- Move global.css to app directory

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

src/components/metrics/MetricCard.tsx

@@ -34,8 +34,8 @@ export const MetricCard = ({
       justifyContent="center"
       paddingX="6"
       paddingY="4"
-      borderRadius="3"
-      backgroundColor
+      borderRadius
+      backgroundColor="surface-base"
       border
     >
       {showLabel && (
@@ -43,7 +43,7 @@ export const MetricCard = ({
           {label}
         </Text>
       )}
-      <Text size="8" weight="bold" wrap="nowrap">
+      <Text size="4xl" weight="bold" wrap="nowrap">
         <AnimatedDiv title={value?.toString()}>{props?.x?.to(x => formatValue(x))}</AnimatedDiv>
       </Text>
       {showChange && (