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/Identities/TraitInputTests.cs

@@ -0,0 +1,125 @@
+using System.Text.Json;
+using MicCheck.Api.Identities;
+using NUnit.Framework;
+
+namespace MicCheck.Api.Tests.Unit.Identities;
+
+[TestFixture]
+public class TraitInputTests
+{
+    private static JsonElement ParseElement(string json) => JsonDocument.Parse(json).RootElement;
+
+    [Test]
+    public void WhenTraitValueIsAJsonString_ThenGetStringValueReturnsTheString()
+    {
+        var trait = new TraitInput("plan", ParseElement("\"premium\""));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("premium"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.String));
+    }
+
+    [Test]
+    public void WhenTraitValueIsJsonTrue_ThenGetStringValueReturnsTrueAndTypeIsBoolean()
+    {
+        var trait = new TraitInput("beta", ParseElement("true"));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("true"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Boolean));
+    }
+
+    [Test]
+    public void WhenTraitValueIsJsonFalse_ThenGetStringValueReturnsFalseAndTypeIsBoolean()
+    {
+        var trait = new TraitInput("beta", ParseElement("false"));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("false"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Boolean));
+    }
+
+    [Test]
+    public void WhenTraitValueIsJsonNull_ThenGetStringValueReturnsEmptyString()
+    {
+        var trait = new TraitInput("plan", ParseElement("null"));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo(string.Empty));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAJsonInteger_ThenTypeIsInteger()
+    {
+        var trait = new TraitInput("age", ParseElement("42"));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("42"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Integer));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAJsonFloat_ThenTypeIsFloat()
+    {
+        var trait = new TraitInput("score", ParseElement("4.5"));
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("4.5"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Float));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAJsonArray_ThenGetStringValueFallsBackToToString()
+    {
+        var element = ParseElement("[1,2,3]");
+        var trait = new TraitInput("list", element);
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo(element.ToString()));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.String));
+    }
+
+    [Test]
+    public void WhenTraitValueIsNull_ThenGetStringValueReturnsEmptyStringAndTypeIsString()
+    {
+        var trait = new TraitInput("plan", null);
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo(string.Empty));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.String));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAPlainBool_ThenTypeIsBoolean()
+    {
+        var trait = new TraitInput("beta", true);
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("True"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Boolean));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAPlainInt_ThenTypeIsInteger()
+    {
+        var trait = new TraitInput("age", 42);
+
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Integer));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAPlainLong_ThenTypeIsInteger()
+    {
+        var trait = new TraitInput("age", 42L);
+
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Integer));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAPlainDouble_ThenTypeIsFloat()
+    {
+        var trait = new TraitInput("score", 4.5d);
+
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.Float));
+    }
+
+    [Test]
+    public void WhenTraitValueIsAPlainString_ThenTypeIsString()
+    {
+        var trait = new TraitInput("plan", "premium");
+
+        Assert.That(trait.GetStringValue(), Is.EqualTo("premium"));
+        Assert.That(trait.GetValueType(), Is.EqualTo(TraitValueType.String));
+    }
+}