feat(ci): Add GitHub Actions workflows for test automation and status badges

Add comprehensive test automation setup with GitHub Actions:
- Create test.yml for running tests on main/develop branches
- Add pr-test.yml for PR validation with test results comments
- Add update-badges.yml for dynamic test status badge updates
- Configure code coverage reporting with Codecov integration

Documentation:
- Add BADGE_SETUP.md with instructions for configuring test status badges
- Add WORKFLOWS_GUIDE.md explaining CI/CD workflow setup
- Update README.md with build and test status badges

Test Framework:
- Configure test project to use .NET 9.0
- Set up test coverage reporting with coverlet
- Add integration tests with WireMock for API mocking
- Add unit tests for configuration and HTTP client components
- Document testing strategy in TestingStrategy.md

Build:
- Add Dockerfile.test for containerized testing
- Update .gitignore for test artifacts
- Configure test dependencies in VRCAuthProxy.Tests.csproj

This change enables automated testing on PRs and branches, with visual status indicators and detailed test results in PR comments.

Tests/Unit/HttpClientCookieContainerTests.cs

@@ -0,0 +1,41 @@
+using System.Net;
+using FluentAssertions;
+using Xunit;
+
+namespace VRCAuthProxy.Tests.Unit
+{
+    public class HttpClientCookieContainerTests
+    {
+        [Fact]
+        public void HttpClientCookieContainer_ExposesCookieContainer()
+        {
+            // Arrange
+            var cookieContainer = new CookieContainer();
+            var handler = new HttpClientHandler { CookieContainer = cookieContainer };
+            
+            // Act
+            var client = new HttpClientCookieContainer(handler);
+            
+            // Assert
+            client.CookieContainer.Should().BeSameAs(cookieContainer);
+        }
+        
+        [Fact]
+        public void CookieContainer_CanStoreAndRetrieveCookies()
+        {
+            // Arrange
+            var cookieContainer = new CookieContainer();
+            var uri = new Uri("https://test.com");
+            
+            // Act
+            cookieContainer.Add(uri, new Cookie("auth", "test-auth-token"));
+            
+            // Assert
+            var cookies = cookieContainer.GetCookies(uri);
+            cookies.Count.Should().Be(1);
+            var authCookie = cookies["auth"];
+            authCookie.Should().NotBeNull();
+            authCookie!.Value.Should().Be("test-auth-token");
+        }
+    }
+}