Feature: Add devopsos `doctor` Command

## Title

Add `doctor` command to check DevOps-OS environment

## Why

The quickstart requires Python, Docker, and sometimes VSCode DevContainers. A diagnostic command would help users.

## Example:

`python -m cli.devopsos `doctor`

## Output:

```
✔ Python 3.10+
✔ Docker installed
✔ DevContainer extension detected
✔ CLI dependencies installed
```