`file` command labels both sides with the NEW filename

[n1ckyb]

The bug

intentumdiff file OLD NEW labels both sides with the NEW filename.

printf "def greet(name):\n    return 'hi ' + name\n" > a.py
printf "def greet(name):\n    if not name:\n        return None\n    return 'hi ' + name\n" > b.py
intentumdiff --no-banner file a.py b.py

+---- Semantic diff -----+
| Old       b.py         |     <-- should be a.py
| New       b.py         |
| Language  python       |
| Scope     working tree |     <-- questionable for two local files
| Changes   1            |
+------------------------+

The diff itself is correct — one ADDITION, Insert -> if_statement. Only the header is wrong.

Why it matters more than it looks

This is the first thing a new user sees, and it says the tool compared a file with itself. It
reads as "this tool is broken" before anyone gets as far as the result, which is right
underneath and perfectly good.

Scope: working tree is also misleading for two explicitly named local files — nothing about
that invocation involves a working tree.

Environment

Reproduced against a locally built 0.0.1b1 (release core) on Windows.

Definition of done

• Old shows the first path as given, New the second
• Scope reflects the actual invocation, or is omitted when it does not apply
• A test asserts the header, since the diff being right is clearly not sufficient