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.

Dockerfile.test

@@ -0,0 +1,15 @@
+FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
+
+WORKDIR /app
+
+# Copy csproj and restore dependencies
+COPY *.sln ./
+COPY VRCAuthProxy/*.csproj ./VRCAuthProxy/
+COPY Tests/*.csproj ./Tests/
+RUN dotnet restore
+
+# Copy the remaining files
+COPY . ./
+
+# Run tests
+ENTRYPOINT ["dotnet", "test", "--logger:console"]