Fix Cash account subtype missing from debit-normal balance check

AccountSubType.Cash was not included in IsNormalDebitBalance in both
AccountBalanceService and LedgerService, causing Cash accounts to be
treated as credit-normal. Payments deposited to a Cash account were
debited in the wrong direction, producing a negative balance.

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

src/PowderCoating.Infrastructure/Services/AccountBalanceService.cs

@@ -117,7 +117,8 @@ public class AccountBalanceService : IAccountBalanceService
     /// </summary>
     private static bool IsNormalDebitBalance(AccountSubType subType) => subType switch
     {
-        AccountSubType.Checking
+        AccountSubType.Cash
+            or AccountSubType.Checking
             or AccountSubType.Savings
             or AccountSubType.AccountsReceivable
             or AccountSubType.Inventory

src/PowderCoating.Infrastructure/Services/LedgerService.cs

@@ -349,7 +349,8 @@ public class LedgerService : ILedgerService
     private static bool IsNormalDebitBalance(AccountSubType subType) => subType switch
     {
         // Asset subtypes → normal debit balance
-        AccountSubType.Checking
+        AccountSubType.Cash
+            or AccountSubType.Checking
             or AccountSubType.Savings
             or AccountSubType.AccountsReceivable
             or AccountSubType.Inventory