docs: cross-reference leaderboard duplication, service-role-key warning

- Add cross-reference comments between dashboard-queries.ts computeLeaderboard()
  and dashboard/ui.ts renderLeaderboard() so maintainers know to update both
- Add security note in setup-team-dashboard about service-role-key visibility
  in pg_cron job table

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/dashboard-queries.ts

@@ -228,6 +228,9 @@ export function computeCostTrend(evalRuns: Record<string, unknown>[]): CostTrend
   return { weekly, totalAllTime };
 }
 
+// NOTE: The dashboard UI (supabase/functions/dashboard/ui.ts renderLeaderboard())
+// has a parallel client-side implementation of this logic. If you change the
+// aggregation or sorting here, update the dashboard JS too.
 /**
  * Compute team leaderboard for the current week.
  */