fix(test): add required round_positions to hub driver fixtures from pre-#24 branches

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/test/h2h.test.ts

@@ -18,6 +18,7 @@ function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
     cumulative: [],
     teammate_wins: 9,
     teammate_losses: 1,
+    round_positions: [],
     ...over,
   }
 }