MkDir creates the parent of the requested directory, and nothing at all for the documented example

`MkDir` creates the parent of the directory it is asked for, not the directory itself. For the example in the docs it creates nothing at all and reports success.

`docs/actions.md` documents the argument as a directory:

```
* Arg1[str]: Full path name of directory

MkDir: ['C:\Glazier_Cache']
```

`MkDir.Run()` passes that straight to `file_util.CreateDirectories()` (`file_system.py:127`), whose own docstring describes a different kind of argument:

```python
"""Create directory if the path to a file doesn't exist.

Args:
path: The full file path to where a file will be placed.
"""
dirname = os.path.dirname(path)
if not os.path.isdir(dirname):
os.makedirs(dirname)
```

So the last component is stripped. Measured on CPython 3.13.13:

```python
file_util.CreateDirectories(r'...\Glazier_Cache')
# target exists after call? False
# parent exists after call? True
```

For the documented example the effect is silence rather than a wrong directory, because `os.path.dirname(r'C:\Glazier_Cache')` is `'C:\'`, which already exists, so the `isdir` guard short-circuits and nothing is created. No exception is raised, so the build step reports success.

This is not platform-specific. `os.path.dirname('/Glazier_Cache')` is `'/'` on POSIX and behaves the same way.

The two docstrings are each self-consistent, so the defect is the pairing: `CreateDirectories` is a "make room for this file" helper and `MkDir` is documented as "make this directory". Either `MkDir` should pass `os.path.join(path, '')`, or it needs its own call to `os.makedirs`.

I have no Linux or macOS machine, so the POSIX sentence above is read from `posixpath` semantics rather than measured.

Read docs/actions.md and trace MkDir.Run() to file_system.py:127, then reproduce the documented path behavior on the supported platforms. Verify that the requested directory exists after the action, that existing-directory handling still succeeds, and that the relevant MkDir or file utility tests pass.

Written by the indexing model from the issue text.