feat(usage): add account cost to breakdown sub-table and admin usage log

- UserBreakdownItem: add AccountCost field + SQL aggregation
- UserBreakdownSubTable: add orange account cost column
- Admin usage table: add account_cost column (after cost, default visible)
- Column settings: add account_cost toggle option

backend/internal/repository/usage_log_repo.go

@@ -3157,7 +3157,8 @@ func (r *usageLogRepository) GetUserBreakdownStats(ctx context.Context, startTim
 			COUNT(*) as requests,
 			COALESCE(SUM(ul.input_tokens + ul.output_tokens + ul.cache_creation_tokens + ul.cache_read_tokens), 0) as total_tokens,
 			COALESCE(SUM(ul.total_cost), 0) as cost,
-			COALESCE(SUM(ul.actual_cost), 0) as actual_cost
+			COALESCE(SUM(ul.actual_cost), 0) as actual_cost,
+			COALESCE(SUM(COALESCE(ul.account_stats_cost, ul.total_cost) * COALESCE(ul.account_rate_multiplier, 1)), 0) as account_cost
 		FROM usage_logs ul
 		LEFT JOIN users u ON u.id = ul.user_id
 		WHERE ul.created_at >= $1 AND ul.created_at < $2
@@ -3228,6 +3229,7 @@ func (r *usageLogRepository) GetUserBreakdownStats(ctx context.Context, startTim
 			&row.TotalTokens,
 			&row.Cost,
 			&row.ActualCost,
+			&row.AccountCost,
 		); err != nil {
 			return nil, err
 		}