GSP Linux Agent Panel Integration

Workspace reference: GSP-WORKSPACE.md

The Panel is authoritative. The Linux agent executes the work the Panel requests.

Legacy Workshop RPC

The dedicated Panel steam_workshop module still uses the legacy steam_workshop XML-RPC call.

Current compatibility rule:

if the Panel sends a blank config_file_path, the Linux agent runs post-install logic only
the generated script must skip all cat / regex / config-write logic in that case
WorkshopModsInfo is still written so the Panel can list/uninstall installed items even when no game config file is edited
new installs write per-home records under WorkshopModsInfo/home_<home_id>/
each record stores mod string, Workshop item ID, title, installed folder/path, Workshop App ID, install status, and timestamps
the generated job writes <game_home>/WorkshopInstallStatus.json as running, completed, or failed
the generated job prints GSP_WORKSHOP_INSTALL_COMPLETE or GSP_WORKSHOP_INSTALL_FAILED so the Panel can avoid stale Update in progress displays if the generic update screen lingers