harper-cli lint should output full path to input files

**Describe the bug**
harper-cli's lint output contains just the basename of each file checked. There are two problems with this:
- it makes it hard to understand which file each message is for, when there are many files with the same basename among the linted ones, for example ./foo.md bar/foo.md quux/baz/foo.md (all of these are reported as just foo.md)
- it makes it hard to find the file in question if it's in a subdir somewhere

**To Reproduce**
```
cd to-a-dir-containing-markdown-files-in-various-subdirs
harper-cli lint $(find . -name "*.md")
```

**Expected behavior**
Output with full paths to input files as given, e.g. ./foo.md, ./some/sub/dir/bar.md, etc.

**Screenshots**
N/A

**Platform**
CLI

**Additional context**
N/A

Start at the harper-cli lint command and trace how the input paths from the command line are represented in its output. Reproduce the issue with markdown files in multiple subdirectories, then verify that output preserves each path as supplied, including its directory components.

Written by the indexing model from the issue text.