Improve error diagnostics for search_central_via_connection when search_path is None

[Copilot]

When search_path is None (Google Drive root case), the error message rendered as Error searching files at — no location context, making failures undiagnosable from logs.

Changes

• datashuttle/utils/folders.py: Introduce display_search_path inside the if output.returncode != 0: block only — keeping it out of the hot path
  • When search_path is None: resolves to f"{rclone_config_name}:<root>" (e.g. gdrive-config:<root>)
  • Otherwise: uses final_search_path as before

if output.returncode != 0:
    display_search_path = (
        f"{rclone_config_name}:<root>"
        if search_path is None
        else final_search_path
    )
    utils.log_and_message(
        f"Error searching files at {display_search_path}\n"
        ...
    )

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