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/page.tsx

@@ -0,0 +1,49 @@
+import { cached } from '@/app/cached-functions'
+import { Totals } from '@/app/groups/[groupId]/stats/totals'
+import {
+  Card,
+  CardContent,
+  CardDescription,
+  CardHeader,
+  CardTitle,
+} from '@/components/ui/card'
+import { getGroupExpenses } from '@/lib/api'
+import { getTotalGroupSpending } from '@/lib/totals'
+import { Metadata } from 'next'
+import { notFound } from 'next/navigation'
+
+export const metadata: Metadata = {
+  title: 'Totals',
+}
+
+export default async function TotalsPage({
+  params: { groupId },
+}: {
+  params: { groupId: string }
+}) {
+  const group = await cached.getGroup(groupId)
+  if (!group) notFound()
+
+  const expenses = await getGroupExpenses(groupId)
+  const totalGroupSpendings = getTotalGroupSpending(expenses)
+
+  return (
+    <>
+      <Card className="mb-4">
+        <CardHeader>
+          <CardTitle>Totals</CardTitle>
+          <CardDescription>
+            Spending summary of the entire group.
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="flex flex-col space-y-4">
+          <Totals
+            group={group}
+            expenses={expenses}
+            totalGroupSpendings={totalGroupSpendings}
+          />
+        </CardContent>
+      </Card>
+    </>
+  )
+}