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.Infrastructure/Repositories/BillRepository.cs

@@ -0,0 +1,40 @@
+using Microsoft.EntityFrameworkCore;
+using PowderCoating.Core.Entities;
+using PowderCoating.Core.Interfaces.Repositories;
+using PowderCoating.Infrastructure.Data;
+
+namespace PowderCoating.Infrastructure.Repositories;
+
+/// <summary>
+/// Typed repository for <see cref="Bill"/> that provides domain-specific multi-level
+/// include queries previously expressed inline in <c>BillsController</c>.
+/// </summary>
+public class BillRepository : Repository<Bill>, IBillRepository
+{
+    public BillRepository(ApplicationDbContext context) : base(context) { }
+
+    /// <inheritdoc/>
+    public async Task<Bill?> LoadForViewAsync(int id)
+    {
+        return await _context.Bills
+            .Where(b => b.Id == id && !b.IsDeleted)
+            .Include(b => b.Vendor)
+            .Include(b => b.APAccount)
+            .Include(b => b.LineItems.Where(li => !li.IsDeleted))
+                .ThenInclude(li => li.Account)
+            .Include(b => b.LineItems.Where(li => !li.IsDeleted))
+                .ThenInclude(li => li.Job)
+            .Include(b => b.Payments.Where(p => !p.IsDeleted))
+                .ThenInclude(p => p.BankAccount)
+            .FirstOrDefaultAsync();
+    }
+
+    /// <inheritdoc/>
+    public async Task<Bill?> LoadForEditAsync(int id)
+    {
+        return await _context.Bills
+            .Where(b => b.Id == id && !b.IsDeleted)
+            .Include(b => b.LineItems.Where(li => !li.IsDeleted))
+            .FirstOrDefaultAsync();
+    }
+}