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/ConfigTests.cs

@@ -0,0 +1,125 @@
+using System.Text.Json;
+using FluentAssertions;
+using Xunit;
+
+namespace VRCAuthProxy.Tests.Unit
+{
+    public class ConfigTests
+    {
+        [Fact]
+        public void Config_LoadsAccountsFromJsonFile()
+        {
+            // Arrange
+            var tempFile = Path.GetTempFileName();
+            var configData = new 
+            {
+                accounts = new object[]
+                {
+                    new { username = "user1", password = "pass1", totpSecret = "secret1" },
+                    new { username = "user2", password = "pass2" }
+                }
+            };
+            
+            File.WriteAllText(tempFile, JsonSerializer.Serialize(configData));
+            
+            try
+            {
+                // Override the default config path for testing
+                string originalConfigPath = Path.Combine(AppContext.BaseDirectory, "appsettings.json");
+                string backupPath = originalConfigPath + ".bak";
+                
+                if (File.Exists(originalConfigPath))
+                {
+                    File.Move(originalConfigPath, backupPath, true);
+                }
+                
+                File.Copy(tempFile, originalConfigPath, true);
+                
+                // Act
+                var config = Config.Load();
+                
+                // Assert
+                config.Should().NotBeNull();
+                config.Accounts.Should().HaveCount(2);
+                
+                config.Accounts[0].username.Should().Be("user1");
+                config.Accounts[0].password.Should().Be("pass1");
+                config.Accounts[0].totpSecret.Should().Be("secret1");
+                
+                config.Accounts[1].username.Should().Be("user2");
+                config.Accounts[1].password.Should().Be("pass2");
+                config.Accounts[1].totpSecret.Should().BeNull();
+                
+                // Restore original config
+                if (File.Exists(backupPath))
+                {
+                    File.Move(backupPath, originalConfigPath, true);
+                }
+            }
+            finally
+            {
+                // Clean up the temp file
+                if (File.Exists(tempFile))
+                {
+                    File.Delete(tempFile);
+                }
+            }
+        }
+        
+        [Fact]
+        public void Config_Save_WritesConfigToFile()
+        {
+            // Arrange
+            var tempFile = Path.GetTempFileName();
+            var originalConfigPath = Path.Combine(AppContext.BaseDirectory, "appsettings.json");
+            var backupPath = originalConfigPath + ".bak";
+            
+            if (File.Exists(originalConfigPath))
+            {
+                File.Move(originalConfigPath, backupPath, true);
+            }
+            
+            File.Copy(tempFile, originalConfigPath, true);
+            
+            try
+            {
+                var config = new Config
+                {
+                    Accounts = new List<ConfigAccount>
+                    {
+                        new ConfigAccount { username = "test1", password = "pass1", totpSecret = "secret1" }
+                    }
+                };
+                
+                // Act
+                config.Save();
+                
+                // Assert
+                File.Exists(originalConfigPath).Should().BeTrue();
+                
+                var loadedConfig = JsonSerializer.Deserialize<iConfig>(File.ReadAllText(originalConfigPath));
+                if (loadedConfig != null)
+                {
+                    loadedConfig.accounts.Should().HaveCount(1);
+                    loadedConfig.accounts[0].username.Should().Be("test1");
+                    loadedConfig.accounts[0].password.Should().Be("pass1");
+                    loadedConfig.accounts[0].totpSecret.Should().Be("secret1");
+                }
+                
+                // Restore original config
+                if (File.Exists(backupPath))
+                {
+                    File.Move(backupPath, originalConfigPath, true);
+                }
+            }
+            finally
+            {
+                // Clean up the temp file
+                if (File.Exists(tempFile))
+                {
+                    File.Delete(tempFile);
+                }
+            }
+        }
+    }
+}