Executes a shell command via /bin/sh -c with a configurable timeout.
Arguments:
command(required) — the shell command.timeout_ms(optional, default 120_000, max 600_000).
Returns captured stdout+stderr plus the exit code. Timeouts kill the spawned
process and surface {:error, :timeout} to the loop.
Runs with cd: ctx.cwd, stderr_to_stdout: true. No input redirection.