Check pip packages match requirements.txt

[vidya381]

Knowing the venv exists is good but not enough. Packages inside might be outdated or missing. When a Python project is detected and a venv exists, check if installed packages match requirements.txt.

Run pip check inside the venv or compare pip freeze output against requirements.txt. Fail if there are missing or incompatible packages.

Add to internal/check/deps.go or a separate internal/check/pipdeps.go.