Document SSH host identity and canonical NG preview

[folker]

What changed

• document the RCC SSH host-certification-authority model and RCC Connect migration workflow
• update safe-access, VS Code, rollout, and security guidance for the new host-identity model
• expose the new policy in both supported navigation definitions
• identify the custom RCC renderer as the canonical ClusterDocs NG preview
• acknowledge past RCC team members on the Who we are page

Why

The NG documentation needs to reflect the revised machine-credential design while retaining the RCC-styled frontend used on port 8765. Explicit preview instructions prevent the generic MkDocs theme from being mistaken for the intended site.

Impact

Users receive consistent guidance for verifying RCC hosts, repairing connections, using VS Code, and choosing trusted endpoints. Maintainers can reproduce the canonical local preview with the same renderer used by validation and deployment.

Validation

• python tools/validate_repo.py
• python -m pytest -q --ignore=site-preview --ignore=site-test — 43 passed
• generated-site link validation — passed
• live checks of the homepage, SSH policy, and Who we are page on port 8765