Invert liability graphs to have correct signage (#1928)

Author: zachgoll

app/models/account/chartable.rb

@@ -14,6 +14,7 @@ def balance_series(currency:, period: Period.last_30_days, favorable_direction:
       ])
 
       balances = gapfill_balances(balances)
+      balances = invert_balances(balances) if favorable_direction == "down"
 
       values = [ nil, *balances ].each_cons(2).map do |prev, curr|
         Series::Value.new(
@@ -69,6 +70,13 @@ def balance_series_query
         SQL
       end
 
+      def invert_balances(balances)
+        balances.map do |balance|
+          balance.balance = -balance.balance
+          balance
+        end
+      end
+
       def gapfill_balances(balances)
         gapfilled = []