feat: initialise a new totals tab with basic UI (#94)

* feat: initialise a new totals tab with basic UI

* fix: update group tabs and add stats page

* fix: styling within the new elements

* Prettier

* Display active user expenses only if active user is set

---------

Co-authored-by: Sebastien Castiel <sebastien@castiel.me>

src/app/groups/[groupId]/stats/totals-group-spending.tsx

@@ -0,0 +1,17 @@
+import { formatCurrency } from '@/lib/utils'
+
+type Props = {
+  totalGroupSpendings: number
+  currency: string
+}
+
+export function TotalsGroupSpending({ totalGroupSpendings, currency }: Props) {
+  return (
+    <div>
+      <div className="text-muted-foreground">Total group spendings</div>
+      <div className="text-lg">
+        {formatCurrency(currency, totalGroupSpendings)}
+      </div>
+    </div>
+  )
+}