Refactor: centralize accounting helpers, status constants, and query deduplication

- AccountingDropdownHelper: wired into BillsController and ExpensesController,
  replacing 35-40 lines of duplicated DB queries per controller
- AppConstants.StatusCodes: added Job.* and Quote.* constants to replace all
  magic status strings across Jobs, Quotes, Appointments, OvenScheduler,
  AiQuickQuote, QuoteApproval, and AccountingDropdownHelper
- AccountingRules: extracted IsNormalDebitBalance into shared Infrastructure
  helper; removed duplicate private method from AccountBalanceService and
  LedgerService (~50 lines deleted)
- AccountDataExportController: extracted 9 Fetch*Async methods (superset of
  includes) so Add*Sheet and Build*Csv no longer duplicate DB queries; each
  entity is queried once regardless of whether XLSX or CSV format is requested
- BillsController.Create and ExpensesController.Create wrapped in
  ExecuteInTransactionAsync; blob uploads moved after commit to keep
  financial data atomic and prevent orphaned blobs from rolling back
- Number generators (Appointments, CreditMemo, OvenBatch) fixed from full-table
  GetAllAsync to prefix-filtered FindAsync

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

src/PowderCoating.Infrastructure/Services/LedgerService.cs

@@ -306,7 +306,7 @@ public class LedgerService : ILedgerService
 
         // Derive normal-debit-balance flag from AccountSubType (more authoritative than AccountType,
         // since users could misconfigure AccountType while SubType is picked from a constrained list).
-        bool normalDebitBalance = IsNormalDebitBalance(account.AccountSubType);
+        bool normalDebitBalance = AccountingRules.IsNormalDebitBalance(account.AccountSubType);
 
         // Compute the balance before the selected period
         decimal priorBalance = await ComputePriorBalanceAsync(account, fromDate, to.Date, normalDebitBalance);
@@ -338,36 +338,6 @@ public class LedgerService : ILedgerService
         };
     }
 
-    /// <summary>
-    /// Returns <c>true</c> if the account sub-type has a normal debit balance (Assets, Expenses, COGS),
-    /// <c>false</c> for normal credit balance (Liabilities, Equity, Revenue).
-    /// <see cref="AccountSubType"/> is used rather than <see cref="PowderCoating.Core.Enums.AccountType"/>
-    /// because sub-type is constrained to a known set of values and cannot be misconfigured by a user,
-    /// whereas <c>AccountType</c> is a broader category that a user might set incorrectly.
-    /// Expense enum values are ≥ 50 by convention, allowing a catch-all range match.
-    /// </summary>
-    private static bool IsNormalDebitBalance(AccountSubType subType) => subType switch
-    {
-        // Asset subtypes → normal debit balance
-        AccountSubType.Cash
-            or AccountSubType.Checking
-            or AccountSubType.Savings
-            or AccountSubType.AccountsReceivable
-            or AccountSubType.Inventory
-            or AccountSubType.FixedAsset
-            or AccountSubType.OtherCurrentAsset
-            or AccountSubType.OtherAsset => true,
-
-        // COGS → normal debit balance
-        AccountSubType.CostOfGoodsSold => true,
-
-        // Expense subtypes (enum values ≥ 50) → normal debit balance
-        var st when (int)st >= 50 => true,
-
-        // Liability subtypes (AP, CreditCard, etc.), Equity, Revenue → normal credit balance
-        _ => false
-    };
-
     /// <summary>
     /// Computes the account balance on the day immediately before <paramref name="beforeDate"/>
     /// by summing all activity prior to that date across every transaction source and adding
@@ -375,7 +345,7 @@ public class LedgerService : ILedgerService
     /// date is on or before <paramref name="periodEnd"/> — a future-dated opening balance (e.g.
     /// from a mid-year chart-of-accounts migration) should not pollute earlier period reports.
     /// A null <c>OpeningBalanceDate</c> means the balance predates all transactions and always applies.
-    /// The sign convention follows <see cref="IsNormalDebitBalance"/>: debits increase debit-normal
+    /// The sign convention follows <see cref="AccountingRules.IsNormalDebitBalance"/>: debits increase debit-normal
     /// accounts and credits increase credit-normal accounts.
     /// </summary>
     private async Task<decimal> ComputePriorBalanceAsync(