Windows and Linux build environments; check clean on both (E-01)

MuPDF builds with MSBuild on Windows (/MT, OpenSSL from vcpkg);
Git for Windows' MinGit stands in for the source build there. CEF
loads from where libcef lives and sets its API version first on
every platform. File identity on Windows compares volume and index.
The checkout and reference/ keep LF on Windows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ely-platform/src/install.rs

@@ -3,8 +3,9 @@
 use std::{
     io,
     path::{Path, PathBuf},
-    process::{Command, Stdio},
 };
+#[cfg(target_os = "macos")]
+use std::process::{Command, Stdio};
 
 /// The `.app` running this process; none in dev builds.
 pub fn running_bundle() -> io::Result<Option<PathBuf>> {
@@ -50,6 +51,7 @@ fn stage(from: &Path, parent: &Path, name: &std::ffi::OsStr) -> io::Result<PathB
 }
 
 /// Puts `staged` at `bundle`; on failure the old returns.
+#[cfg(any(target_os = "macos", test))]
 fn swap(staged: &Path, bundle: &Path) -> io::Result<()> {
     let name = bundle.file_name().ok_or_else(|| io::Error::other("the app has no name"))?;
     let old = bundle.with_file_name(format!(".{}.old", name.to_string_lossy()));