make os mv and cp commands non interactive (#430)

- fix(fs): handle NFS permission errors with robust fallback - Catch
PermissionError/OSError(EPERM) in atomic_move and atomic_copy -
Implement layered fallback: shutil.copyfile (content only) -> system
mv/cp - Add _perform_nfs_fallback and _system_op helpers to reduce
duplication - Set fallback logging to DEBUG to reduce spam on NFS mounts
- make os mv and cp commands non interactive (-f)

shelfmark/download/fs.py

@@ -63,7 +63,7 @@ def _system_op(op: str, source: Path, dest: Path) -> None:
     """Execute system command (mv or cp) as final fallback."""
     logger.info(f"Attempting system {op} as final fallback: {source} -> {dest}")
     subprocess.run(
-        [op, str(source), str(dest)],
+        [op, "-f", str(source), str(dest)],
         check=True,
         capture_output=True,
         text=True