feat(giving): single-entry giving service with paging + lock guard

Adds GivingListItemDto, GivingDto, CreateGivingRequest, UpdateGivingRequest DTOs;
IGivingService interface; GivingService implementation with category/date filtering,
OfferingSession lock guard (Submitted/Reconciled), and DI registration in Program.cs.
Covered by 4 xUnit tests (TDD: red → green).

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

API/ROLAC.API.Tests/Services/GivingServiceTests.cs

@@ -0,0 +1,103 @@
+using Microsoft.EntityFrameworkCore;
+using System.Security.Claims;
+using Microsoft.AspNetCore.Http;
+using Moq;
+using ROLAC.API.Data;
+using ROLAC.API.Data.Interceptors;
+using ROLAC.API.DTOs.Giving;
+using ROLAC.API.Entities;
+using ROLAC.API.Services;
+using Xunit;
+
+namespace ROLAC.API.Tests.Services;
+
+public class GivingServiceTests
+{
+    private static IHttpContextAccessor BuildAccessor(string userId = "test-user")
+    {
+        var claims = new[] { new Claim(ClaimTypes.NameIdentifier, userId) };
+        var ctx    = new DefaultHttpContext { User = new(new ClaimsIdentity(claims)) };
+        var mock   = new Mock<IHttpContextAccessor>();
+        mock.Setup(x => x.HttpContext).Returns(ctx);
+        return mock.Object;
+    }
+
+    private static AppDbContext BuildDb(string userId = "test-user")
+    {
+        var interceptor = new AuditSaveChangesInterceptor(BuildAccessor(userId));
+        return new AppDbContext(
+            new DbContextOptionsBuilder<AppDbContext>()
+                .UseInMemoryDatabase(Guid.NewGuid().ToString())
+                .AddInterceptors(interceptor)
+                .Options);
+    }
+
+    private static async Task<int> SeedCategoryAsync(AppDbContext db)
+    {
+        var c = new GivingCategory { Name_en = "Tithe", IsActive = true };
+        db.GivingCategories.Add(c);
+        await db.SaveChangesAsync();
+        return c.Id;
+    }
+
+    [Fact]
+    public async Task CreateAsync_PersistsGiving()
+    {
+        using var db = BuildDb();
+        var catId = await SeedCategoryAsync(db);
+        var svc = new GivingService(db);
+
+        var id = await svc.CreateAsync(new CreateGivingRequest
+        {
+            GivingCategoryId = catId, Amount = 100m, PaymentMethod = "Cash",
+            GivingDate = new DateOnly(2026, 5, 31), IsAnonymous = true,
+        });
+
+        var saved = await db.Givings.FindAsync(id);
+        Assert.NotNull(saved);
+        Assert.Equal(100m, saved!.Amount);
+        Assert.Null(saved.OfferingSessionId);
+    }
+
+    [Fact]
+    public async Task GetPagedAsync_FiltersByCategory()
+    {
+        using var db = BuildDb();
+        var catId = await SeedCategoryAsync(db);
+        var svc = new GivingService(db);
+        await svc.CreateAsync(new CreateGivingRequest { GivingCategoryId = catId, Amount = 10m, PaymentMethod = "Cash", GivingDate = new DateOnly(2026,5,31) });
+
+        var page = await svc.GetPagedAsync(1, 20, null, catId, null, null);
+
+        Assert.Equal(1, page.TotalCount);
+        Assert.Equal("Tithe", page.Items[0].CategoryName);
+    }
+
+    [Fact]
+    public async Task UpdateAsync_Throws_WhenGivingBelongsToSubmittedSession()
+    {
+        using var db = BuildDb();
+        var catId = await SeedCategoryAsync(db);
+        var session = new OfferingSession { SessionDate = new DateOnly(2026,5,31), Status = "Submitted" };
+        db.OfferingSessions.Add(session);
+        await db.SaveChangesAsync();
+        var giving = new Giving { GivingCategoryId = catId, Amount = 50m, PaymentMethod = "Cash",
+            GivingDate = new DateOnly(2026,5,31), OfferingSessionId = session.Id };
+        db.Givings.Add(giving);
+        await db.SaveChangesAsync();
+
+        var svc = new GivingService(db);
+
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            svc.UpdateAsync(giving.Id, new UpdateGivingRequest
+            { GivingCategoryId = catId, Amount = 999m, PaymentMethod = "Cash", GivingDate = new DateOnly(2026,5,31) }));
+    }
+
+    [Fact]
+    public async Task DeleteAsync_Throws_WhenMissing()
+    {
+        using var db = BuildDb();
+        var svc = new GivingService(db);
+        await Assert.ThrowsAsync<KeyNotFoundException>(() => svc.DeleteAsync(999));
+    }
+}