dsh-gamemode: Switch DeepSeek Harness Agent presets via /gamemode

dsh-gamemode is a slash command plugin for DeepSeek Harness (DSH), designed to allow users to quickly switch agent presets via command before starting a new session, without relying on manual selection through the Web UI. The plugin supports switching to "Creative Mode" (cordis preset) via `/gamemode 1` (or `creative`), switching to "Survival Mode" (standard preset) via `/gamemode 0` (or `survival`), and viewing the current preset using `/gamemode`. Its core functionality involves remounting the live agent to the target preset's standing mount and recording the selection state to ensure the same configuration is reconstructed when resuming or forking sessions.