Add comprehensive test suite infrastructure

- Create backend xUnit test project with Moq and FluentAssertions
- Add test utilities: TestDataFactory, MockHttpContext, TestUserClaims
- Create AuthControllerTests with comprehensive auth scenarios
- Install Jest and React Testing Library for frontend
- Configure jest.config.ts and jest.setup.ts with Next.js support
- Add test scripts to package.json

backend/backend.Tests/.gitignore

@@ -0,0 +1,17 @@
+# Test artifacts
+TestResults/
+coverage/
+*.coverage
+*.trx
+
+# Build outputs
+bin/
+obj/
+
+# IDE
+.idea/
+.vscode/
+
+# OS
+.DS_Store
+Thumbs.db