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/Helpers/TestSetup.cs

@@ -0,0 +1,45 @@
+using System.Net;
+using WireMock.Server;
+
+namespace VRCAuthProxy.Tests.Helpers
+{
+    public class TestSetup : IDisposable
+    {
+        public WireMockServer MockVRChatApi { get; private set; }
+
+        public TestSetup()
+        {
+            // Start WireMock server to mock VRChat API
+            MockVRChatApi = WireMockServer.Start();
+        }
+
+        public void Dispose()
+        {
+            MockVRChatApi?.Dispose();
+        }
+
+        /// <summary>
+        /// Creates a test configuration with mock accounts
+        /// </summary>
+        public static Config CreateTestConfig()
+        {
+            var config = new Config();
+            config.Accounts = new List<ConfigAccount>
+            {
+                new ConfigAccount
+                {
+                    username = "testuser1",
+                    password = "testpassword1",
+                    totpSecret = "TESTSECRET1"
+                },
+                new ConfigAccount
+                {
+                    username = "testuser2",
+                    password = "testpassword2"
+                }
+            };
+            
+            return config;
+        }
+    }
+}