When bat is built without the `git` feature, `StyleComponent::Changes`
is not available. Add `#[cfg(feature = "git")]` guard so `--diff --plain`
works in both configurations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
When --plain is set (via CLI or config file), --diff output loses all
visual markers, making it indistinguishable from plain text. The diff
line filtering still works, but without Changes markers or Snip
separators the output is not useful.
Automatically include Changes and Snip style components when --diff is
active alongside --plain. This preserves the --plain intent (no grid,
no header, no line numbers) while keeping diff output readable.
Closes#3630