Add unit tests for Environments, Audit, and Webhooks namespaces (#6)

## Summary
- Add missing unit test coverage for the Environments, Audit, and Webhooks namespaces (raises them from ~0-62% to 91-100%)
- Exclude WebhookBackgroundService/WebhookRetryBackgroundService from coverage (require live DI/DB, disallowed by CLAUDE.md's no-InMemory/WebApplicationFactory rule)

## Test plan
- [x] `dotnet test` full suite passes (646/646)
- [x] Coverage report confirms Environments ~99.5%, Audit 100%, Webhooks ~91%

Reviewed-on: #6

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

@@ -0,0 +1,58 @@
+using MicCheck.Api.Organizations;
+using MicCheck.Api.Users;
+using NUnit.Framework;
+
+namespace MicCheck.Api.Tests.Unit.Organizations;
+
+[TestFixture]
+public class OrganizationResponseTests
+{
+    [Test]
+    public void WhenMappingAnOrganizationWithoutSpecifyingPrimary_ThenIsPrimaryDefaultsToFalse()
+    {
+        var org = new Organization { Id = 1, Name = "My Org", CreatedAt = DateTimeOffset.UtcNow };
+
+        var response = OrganizationResponse.From(org);
+
+        Assert.That(response.Id, Is.EqualTo(1));
+        Assert.That(response.Name, Is.EqualTo("My Org"));
+        Assert.That(response.IsPrimary, Is.False);
+    }
+
+    [Test]
+    public void WhenMappingAnOrganizationAsPrimary_ThenIsPrimaryIsTrue()
+    {
+        var org = new Organization { Id = 1, Name = "My Org", CreatedAt = DateTimeOffset.UtcNow };
+
+        var response = OrganizationResponse.From(org, isPrimary: true);
+
+        Assert.That(response.IsPrimary, Is.True);
+    }
+}
+
+[TestFixture]
+public class OrganizationMemberResponseTests
+{
+    [Test]
+    public void WhenMappingAMember_ThenFieldsAreSourcedFromTheAssociatedUser()
+    {
+        var user = new User
+        {
+            Id = 1,
+            Email = "alice@example.com",
+            PasswordHash = "hashed",
+            FirstName = "Alice",
+            LastName = "Smith",
+            CreatedAt = DateTimeOffset.UtcNow
+        };
+        var member = new OrganizationUser { OrganizationId = 1, UserId = 1, Role = OrganizationRole.Admin, User = user };
+
+        var response = OrganizationMemberResponse.From(member);
+
+        Assert.That(response.UserId, Is.EqualTo(1));
+        Assert.That(response.FirstName, Is.EqualTo("Alice"));
+        Assert.That(response.LastName, Is.EqualTo("Smith"));
+        Assert.That(response.Email, Is.EqualTo("alice@example.com"));
+        Assert.That(response.Role, Is.EqualTo("Admin"));
+    }
+}