docs: cross-link GitOps Drift hero demo to reproduction guide

[jordigilh]

Context

docs/whats-new/index.md embeds the GitOps Drift hero demo video (interactive mode, production approval gate) but doesn't link to how to reproduce it. docs/use-cases/index.md already links the gitops-drift catalog row out to kubernaut-demo-scenarios, but it isn't called out as the featured/hero scenario, so it doesn't stand out from the other 30+ rows.

Proposal

• Add a "Try it yourself →" link under the video paragraph in whats-new/index.md, pointing to the scenario's walkthrough in kubernaut-demo-scenarios (canonical source of truth for reproduction steps -- see Standardize scenario README structure: separate reader walkthrough from contributor artifacts (pilot: gitops-drift) kubernaut-demo-scenarios#400 for a README rewrite in progress to make that page a better landing target).
• Annotate/elevate the gitops-drift row in use-cases/index.md's catalog table to flag it as the featured hero-demo scenario.

We deliberately are not duplicating the walkthrough into this repo -- the scenario README in kubernaut-demo-scenarios is updated by the same commits that change the scenario's scripts/manifests, so it can't drift the way a mirrored copy here could.

Related

• Standardize scenario README structure: separate reader walkthrough from contributor artifacts (pilot: gitops-drift) kubernaut-demo-scenarios#400 -- README rewrite so the scenario page is a good landing target
• jordigilh/kubernaut -- links to the same guide from the hero demo video in the README