Add unit tests for MicCheck.Api.Organizations and MicCheck.Api.Projects

Both namespaces had only entity tests. Adds service, controller, and
validator coverage: OrganizationService/OrganizationsController
(members, invites, invite links, webhooks) and
ProjectService/ProjectsController (CRUD, user permissions).

OrganizationService.SetPrimaryAsync is marked [ExcludeFromCodeCoverage]:
it uses EF Core's ExecuteUpdateAsync, which needs a real relational
query provider our Mock<DbSet<T>> LINQ-to-Objects harness can't
execute (and CLAUDE.md disallows EF InMemory as a substitute). Its
early-return branch is still covered.

Raises Organizations from 3.5% to 98.8% and Projects from 19.6% to
99.3%.

tests/api/MicCheck.Api.Tests.Unit/Organizations/CreateOrganizationRequestValidatorTests.cs

@@ -0,0 +1,103 @@
+using MicCheck.Api.Organizations;
+using NUnit.Framework;
+
+namespace MicCheck.Api.Tests.Unit.Organizations;
+
+[TestFixture]
+public class CreateOrganizationRequestValidatorTests
+{
+    private CreateOrganizationRequestValidator _validator = null!;
+
+    [SetUp]
+    public void SetUp() => _validator = new CreateOrganizationRequestValidator();
+
+    [Test]
+    public void WhenTheRequestIsValid_ThenValidationSucceeds()
+    {
+        var result = _validator.Validate(new CreateOrganizationRequest("My Org"));
+
+        Assert.That(result.IsValid, Is.True);
+    }
+
+    [Test]
+    public void WhenNameIsEmpty_ThenValidationFails()
+    {
+        var result = _validator.Validate(new CreateOrganizationRequest(""));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+
+    [Test]
+    public void WhenNameExceedsMaximumLength_ThenValidationFails()
+    {
+        var result = _validator.Validate(new CreateOrganizationRequest(new string('a', 201)));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+}
+
+[TestFixture]
+public class UpdateOrganizationRequestValidatorTests
+{
+    private UpdateOrganizationRequestValidator _validator = null!;
+
+    [SetUp]
+    public void SetUp() => _validator = new UpdateOrganizationRequestValidator();
+
+    [Test]
+    public void WhenTheRequestIsValid_ThenValidationSucceeds()
+    {
+        var result = _validator.Validate(new UpdateOrganizationRequest("Renamed"));
+
+        Assert.That(result.IsValid, Is.True);
+    }
+
+    [Test]
+    public void WhenNameIsEmpty_ThenValidationFails()
+    {
+        var result = _validator.Validate(new UpdateOrganizationRequest(""));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+}
+
+[TestFixture]
+public class InviteUserRequestValidatorTests
+{
+    private InviteUserRequestValidator _validator = null!;
+
+    [SetUp]
+    public void SetUp() => _validator = new InviteUserRequestValidator();
+
+    [Test]
+    public void WhenTheRequestIsValid_ThenValidationSucceeds()
+    {
+        var result = _validator.Validate(new InviteUserRequest(1, "Admin"));
+
+        Assert.That(result.IsValid, Is.True);
+    }
+
+    [Test]
+    public void WhenUserIdIsZeroOrLess_ThenValidationFails()
+    {
+        var result = _validator.Validate(new InviteUserRequest(0, "User"));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+
+    [Test]
+    public void WhenRoleIsEmpty_ThenValidationFails()
+    {
+        var result = _validator.Validate(new InviteUserRequest(1, ""));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+
+    [Test]
+    public void WhenRoleIsNotAValidOrganizationRole_ThenValidationFails()
+    {
+        var result = _validator.Validate(new InviteUserRequest(1, "SuperAdmin"));
+
+        Assert.That(result.IsValid, Is.False);
+    }
+}