hello. What is the right way to disable ssh-agent at start? I do not need it.

This usually depends upon your distribution. Which distribution do you use? Many will likely not offer the option to disable it, as it is usually seen as a fairly important component (whilst non-essential for the system itself to operate)

I use Arch.

Unfortunately I'm not aware of how Arch starts ssh-agent. I suggest asking the support methods provided by Arch on how to do this. Alternately, you could kill "ssh-agent" as part of the KDE startup procedure, but that would be a workaround.

ssh-agent -k should do the trick.