Remove failed PRK.Client automation experiment

Remove the abandoned PRK.Client TestHarness and all client-side automation/headless integration so any future attempt starts from scratch. Preserve unrelated renderer tests and ordinary client functionality.\n\nAcceptance criteria:\n- TestHarness, automation smoke tooling, and automation documentation are removed.\n- Client automation protocol/server/controller, build switches, launch flags, and runtime wiring are removed.\n- CI and test project configuration no longer enable or test client automation.\n- PRK.Client builds and relevant tests pass without automation-specific properties. Pull request: #2658 https://git.project-rk.com/prk/engines/pulls/2658