Closes coder/internal#382

The API differs slightly from the RFC, in the interest of making consumption of the API agnostic to the host operating system of the agent.

Queries supply the requested path as an array:

{
  "path": ["home", "coder"],
  "relativity": "root" 
}

Whilst the agent returns the requested path as an OS-specific path string but also as an array, both absolute. (relativity = root)

Linux:

{
    "absolute_path_string": "/home/coder",
    "absolute_path": ["home", "coder"],
    "contents": [
        {
            "absolute_path_string": "/home/coder/.bash_logout",
            "is_dir": false,
            "name": ".bash_logout"
        },
        ...
    ]
}

Windows:

{
    "absolute_path_string": "C:\\Users\\coder",
    "absolute_path": ["C:\\", "Users", "coder"],
    "contents": [
        {
            "absolute_path_string": "C:\\Users\\coder\\Documents",
            "is_dir": true,
            "name": "Documents"
        },
        ...
    ]
}

API consumers need only append the name of a contents to the existing path array in order to query a subdirectory.
To traverse backwards from path: [], relativity=home, the absolute_path array returned can be used, popping the last element off the array, and changing the relativity to root.
Once the consumer has a target, they can use the absolute_path_string - at no point do they need to know the workspace OS.

Example Usage:

$ http POST localhost:4/api/v0/list-directory path:='["home", "coder"]' relativity=root
HTTP/1.1 200 OK
Content-Length: 649
Content-Type: application/json; charset=utf-8
Date: Fri, 28 Feb 2025 05:53:40 GMT

{
    "absolute_path": [
        "home",
        "coder"
    ],
    "absolute_path_string": "/home/coder",
    "contents": [
        {
            "absolute_path_string": "/home/coder/.bash_logout",
            "is_dir": false,
            "name": ".bash_logout"
        },
        ...
    ]
}