The --output option should create subdirs in target dir

### Environment

Node 22.14.0
Automd 0.4.0

### Reproduction

-

### Describe the bug

automd should replicate deep directory structure when generating into another output dir.

Example
``` sh
$ automd --dir src --input "**/*.md" --output ../docs

ERROR  ENOENT: no such file or directory, open '...../docs/sub/sub/index.md'
```

### Additional context

_No response_

### Logs

```sh

```