fix: update document.title on every page via useEffect

All pages are 'use client' so metadata exports don't work. Each page now
sets document.title via useEffect — static pages with a fixed string,
dynamic pages keyed on data so the title reflects the loaded content.

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

app/stats/page.tsx

@@ -1,5 +1,6 @@
 'use client'
 import { useQuery, gql } from '@/lib/graphql/hooks'
+import { useEffect } from 'react'
 import Link from 'next/link'
 import { TeamFlag } from '@/components/team-flag'
 
@@ -57,6 +58,8 @@ interface MatchRow { id: number; year: number; round: string; date?: string | nu
 interface ETStats { totalKnockoutMatches: number; wentToExtraTime: number; wentToPenalties: number; extraTimePct: number; penaltiesPct: number }
 
 export default function StatsPage() {
+  useEffect(() => { document.title = 'Statistics · World Cup' }, [])
+
   const { data, loading } = useQuery(STATS_QUERY)
 
   const tournaments: Tournament[] = (data?.tournaments ?? []).filter((t: Tournament) => t.totalGoals != null).sort((a: Tournament, b: Tournament) => a.year - b.year)