fix(windows): maven package_path mixed OS separator into the reported rel

jar_path was built as leaf_dir.join(&jar_leaf), which inserts an OS
separator (`\` on Windows) before the leaf while the rest of the
reported path keeps the rel's forward slashes — package_path is
reported (and asserted) as a display string, so
wired_rebuild_reports_vendored_jar_path failed on windows-latest.
Join the already-present full forward-slash rel (jar_copy_rel) off
project_root instead; same file, consistent report on every platform.

First-ever windows execution of this test: cargo runs test binaries as
they finish compiling, and every earlier windows run died in some other
binary first.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: mikolalysenko

crates/socket-patch-core/src/patch/vendor/maven_repo.rs

@@ -176,7 +176,11 @@ pub async fn vendor_maven(
     let jar_copy_rel = format!("{leaf_rel}/{jar_leaf}");
     let uuid_dir = project_root.join(&uuid_dir_rel);
     let leaf_dir = project_root.join(&leaf_rel);
-    let jar_path = leaf_dir.join(&jar_leaf);
+    // Join the full forward-slash rel rather than `leaf_dir.join(&jar_leaf)`:
+    // the joined form puts an OS separator (`\` on Windows) before the leaf
+    // while every other reported path keeps the rel's forward slashes —
+    // `package_path` reports (and tests compare) this as a display string.
+    let jar_path = project_root.join(&jar_copy_rel);
     let repo_id = format!("socket-patch-vendor-{}", record.uuid);
 
     // A patch with no files is meaningless to vendor: no-op success, no edits.