Phase 1: Introduce typed repository interfaces and report service stubs

Six IUnitOfWork properties upgraded from generic IRepository<T> to domain-specific
typed interfaces (IJobRepository, IQuoteRepository, IInvoiceRepository,
ICustomerRepository, IBillRepository, IPurchaseOrderRepository). Each backed by a
concrete typed repository that encapsulates complex include chains previously
inlined in controllers.

Also adds IFinancialReportService and IOperationalReportService stub implementations
(NotImplementedException placeholders) to Application.Interfaces and Infrastructure.Services,
registered in Program.cs. These are the migration targets for ReportsController's
aggregate query methods in Phase 2.

No controller behaviour changed in this commit — all callers still compile because
typed interfaces extend IRepository<T>.

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

src/PowderCoating.Application/Interfaces/IFinancialReportService.cs

@@ -0,0 +1,23 @@
+using PowderCoating.Application.DTOs.Accounting;
+
+namespace PowderCoating.Application.Interfaces;
+
+/// <summary>
+/// Read-only service for financial aggregate reports. All methods query the database
+/// with AsNoTracking and return pre-shaped DTOs — no tracked entities are returned.
+/// Implemented in Infrastructure; uses ApplicationDbContext directly.
+/// </summary>
+public interface IFinancialReportService
+{
+    /// <summary>Returns a Profit &amp; Loss report for the given company and date range.</summary>
+    Task<ProfitAndLossDto> GetProfitAndLossAsync(int companyId, DateTime from, DateTime to);
+
+    /// <summary>Returns a Balance Sheet snapshot as of the given date.</summary>
+    Task<BalanceSheetDto> GetBalanceSheetAsync(int companyId, DateTime asOf);
+
+    /// <summary>Returns an AR Aging report bucketed at 0-30, 31-60, 61-90, and 90+ days.</summary>
+    Task<ArAgingReportDto> GetArAgingAsync(int companyId, DateTime asOf);
+
+    /// <summary>Returns a Sales &amp; Income report for the given company and date range.</summary>
+    Task<SalesIncomeReportDto> GetSalesAndIncomeAsync(int companyId, DateTime from, DateTime to);
+}