feat: replace text loading messages with PageSpinner component

Add a shared PageSpinner (spinning ring + optional label) and use it
in all pages that previously showed a plain text loading message:
home, stats, player, team, and tournament pages.

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

components/page-spinner.tsx

@@ -0,0 +1,8 @@
+export function PageSpinner({ label }: { label?: string }) {
+  return (
+    <div className="flex flex-col items-center justify-center gap-4 py-24 text-green-muted">
+      <div className="w-8 h-8 rounded-full border-2 border-green/20 border-t-green animate-spin" />
+      {label && <span className="text-sm tracking-wide">{label}</span>}
+    </div>
+  )
+}