Ln 743 Test Infrastructure

Scaffolds test infrastructure with Vitest for TypeScript, xUnit for .NET, or pytest for Python. Detects your stack, creates config files with 80% coverage thresholds, sets up the right directory structure, and drops in a sample test that actually passes. It's smart about checking what already exists before duplicating work. The AAA pattern enforcement in sample tests is solid, and the coverage threshold config means your CI won't silently rot. Basically handles the boring setup work so you can skip straight to writing real tests. Works well as part of a bootstrap sequence after linting and pre-commit hooks.