- ProcessManager.Start() reads SERVER_BINARY and SERVER_PARAMS from env
with platform-based defaults as fallback
- SteamCmdManager.run() reads STEAMCMD_PATH from env, defaults to
'steamcmd'
- Makefile: add SERVER_BINARY/SERVER_PARAMS/STEAMCMD_PATH variables,
copy stubs to dev-deploy in 'make dev', pass env vars to backend
- .gitignore: add bin/
- ProcessManager: atomic.Int32 state enum (idle/starting/running/stopping)
eliminates race between IsRunning check and Start/Stop
- SteamCmdManager: atomic.Bool with CompareAndSwap for same protection
- Restart() now propagates Stop() errors instead of swallowing them