Fix Windows auto-update to replace Navis.exe in place (1.8.1).

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/update/update.go

@@ -17,7 +17,7 @@ import (
 )
 
 // CurrentVersion is the shipped client version.
-const CurrentVersion = "1.8.0"
+const CurrentVersion = "1.8.1"
 
 // DefaultManifestURL is the update feed (hosted in the project git repo).
 const DefaultManifestURL = "https://git.evilfox.cc/test2/navi/raw/branch/main/dist/update.json"
@@ -250,7 +250,10 @@ func prepareDownload(ctx context.Context, manifestURL string) (latest, url, sha,
 	if err != nil {
 		return "", "", "", "", "", err
 	}
-	tmp := exe + ".new"
+	tmp := filepath.Join(filepath.Dir(exe), ".navis-update-download")
+	_ = os.Remove(tmp)
+	// Also clear legacy leftover from older updaters.
+	_ = os.Remove(exe + ".new")
 	if err := downloadFile(ctx, st.URL, tmp); err != nil {
 		return "", "", "", "", "", err
 	}