🐛 `xaibo init` removes existing venv and forces Python 3.10 even when user wants 3.12

[MFA-X-AI]

Bug Description

When running xaibo init in an existing uv workspace, the command:

1. Removes the existing .venv at the workspace root
2. Forces Python 3.10 even when Python 3.12 is available and preferred

This happens because the init command runs uv init --bare followed by uv add, which triggers uv to recreate the workspace virtual environment, and the generated requires-python = ">=3.10" causes uv to select the lowest compatible Python version.

The current behavior is particularly disruptive because:

1. It destroys the existing venv without warning
2. It silently downgrades Python versions, which can break other tools expecting a newer Python
3. There's no way for the user to control this behavior via CLI arguments

Steps to Reproduce

1. Have an existing uv workspace with a virtual environment
2. Ensure Python 3.12 is available on your system
3. Run:

   uvx xaibo init my_first_agent

4. Select any dependencies (e.g., webserver, openai, livekit)
5. Observe the output:

   Removed virtual environment at: /home/fahreza/Github/xaibo-test-2/.venv
   Creating virtual environment at: /home/fahreza/Github/xaibo-test-2/.venv
   Using CPython 3.10.15 interpreter at: /usr/bin/python3.10
   

Expected Behavior

• The existing venv should be preserved or at least recreated with the same Python version
• OR the user should be able to specify which Python version to use

Actual Behavior

• The venv is removed and recreated
• Python 3.10 is forced even when 3.12 is available

Root Cause Analysis

In src/xaibo/cli/__init__.py:

def init(args, extra_args=[]):
    # ...
    universal_run(f"uv init --bare {project_name}", cwd=curdir)
    universal_run(f"uv add xaibo xaibo[{','.join(modules)}] pytest", cwd=project_dir)

The uv add command in a workspace context triggers uv to sync the workspace environment, which recreates .venv. The generated pyproject.toml has requires-python = ">=3.10", so uv selects Python 3.10 (the lowest compatible version).

Proposed Solutions

Option 1: Add --python argument to init command (Recommended)

Allow users to specify their preferred Python version:

xaibo init my_agent --python 3.12

Implementation:

init_parser.add_argument('--python', type=str, default='3.10',
                        help='Python version to use for the project (default: 3.10)')
# ...
universal_run(f"uv init --bare --python {args.python} {project_name}", cwd=curdir)

Option 2: Detect existing Python version

If a .venv already exists, detect its Python version and preserve it when recreating:

def get_existing_python_version(venv_path):
    """Detect Python version from existing venv if present."""
    python_exe = venv_path / "bin" / "python"
    if python_exe.exists():
        result = subprocess.run([str(python_exe), "--version"], 
                               capture_output=True, text=True)
        # Parse version from output
        return parse_version(result.stdout)
    return None