fix: the server's own folders under a short-named temp path are expanded, not refused (#1055)

On Windows the temporary folder often has an 8.3 short name, which the path scope refuses. vfs::long_names spells folders SolidCraft derives from the environment with long names, and the MCP scratch folder and the recovery folder use it, so screenshot without a path and the recovery commands work there again.

crates/engine/src/cmd/urdf_tests.rs

@@ -96,7 +96,7 @@ fn assert_fk(m: &UrdfModel, s: &Session, what: &str) {
 }
 
 fn temp(tag: &str) -> PathBuf {
-    let d = std::env::temp_dir().join(format!("solidcraft-urdf-{tag}-{}", std::process::id()));
+    let d = solidcraft_io::vfs::temp_dir().join(format!("solidcraft-urdf-{tag}-{}", std::process::id()));
     let _ = std::fs::remove_dir_all(&d);
     let _ = std::fs::create_dir_all(&d);
     d