fix(appimage): bundle libwebkit2gtk-4.1 for SteamOS compatibility

[lobinuxsoft]

Description

AppImages (Hub and Agent) fail on SteamOS (Steam Deck) because libwebkit2gtk-4.1 is not installed. SteamOS is an immutable filesystem — users cannot easily install system packages, and SteamOS updates wipe manually installed packages.

Error

capydeploy-agent-tauri: error while loading shared libraries: libwebkit2gtk-4.1.so.0: cannot open shared object file: No such file or directory

Options

1. Bundle webkit2gtk inside AppImage using linuxdeploy — AppImage grows from ~9MB to ~120MB but works out-of-the-box
2. Document SteamOS dependency with a helper install script (fragile — wiped on SteamOS updates)
3. Both — bundle for fat AppImage, document for users who want minimal

Affected platforms

• SteamOS (Steam Deck) — immutable Arch-based
• Any minimal Linux without webkit2gtk-4.1 installed

Notes

• The Decky plugin is the recommended Agent for Steam Deck gaming mode
• The Tauri Agent on Steam Deck is for desktop mode use cases
• GTK3 is available on SteamOS, only webkit2gtk is missing

[lobinuxsoft]

Completed via PR #201