docs: add Kubernetes-class platform listing roadmap (research)

Studio-side roadmap brief on becoming an official listing on OpenShift
(community Helm chart via chart-verifier), Rancher (SUSE Ready partner
program), and Artifact Hub (Verified Publisher + Official status + Cosign).
Recommends Artifact Hub first (<1 day, best ROI), then the shared chart-
quality fixes that unblock OpenShift and Rancher. 55 cited sources.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: cevheri