Implemented and pushed the isolated Visualizer Stream issue #30 kmssink scaling fix
Impact: Render-node output is software-composed to a fixed 1280x720 canvas before kmssink, with deterministic restart on KMS set-plane warnings and telemetry for decoded size, content rectangle, sink canvas, scaling state, and restarts. Automated and ephemeral GStreamer verification passed; no live or physical display mutation was performed.