Class body byte-identical to original. Module-level IS_SHUTTING_DOWN
flag is mirrored from web_server's own flag in _shutdown_runtime_components
so the monitor loop still sees shutdown signals at the right moment.
Eight web_server-side helpers (_make_context_key, _on_download_completed,
_run_post_processing_worker, _download_track_worker,
_start_next_batch_of_downloads, _orphaned_download_keys,
missing_download_executor, soulseek_client) are injected via init() after
register_runtime_clients, when all symbols are defined and well before
Flask starts accepting requests.
web_server.py: 38220 → 37501 (-719 lines).
