Add Talos Linux and Omni platform guides

[antonflor]

What changed

• Added docs/kubernetes-platforms/talos-linux.md, a current Talos Linux 1.13 operational reference covering:
  • talosctl, contexts, endpoints, nodes, machine configuration, bootstrap, and kubeconfig;
  • health checks, services, logs, support bundles, and runtime resources;
  • Image Factory, system extensions, upgrades, Secure Boot, disk encryption, and KubeSpan;
  • etcd snapshots and recovery, node reset, rollback, and troubleshooting.
• Added docs/kubernetes-platforms/omni.md, a current Omni operational reference covering:
  • the distinction between Sidero Labs, Talos Linux, Omni, SideroLink, and Sidero Metal;
  • machine registration, join tokens, omniconfig, kubeconfig, talosconfig, and access boundaries;
  • cluster templates, machine classes, infrastructure providers, upgrades, backups, audit logs, and recovery;
  • the management-authority handoff that occurs when a Talos machine joins Omni;
  • hosted versus self-hosted deployment and production licensing considerations.
• Added a dedicated Kubernetes platforms section to the repository index.
• Added Mermaid diagrams for the Talos/Omni management boundary and Omni machine-to-cluster lifecycle.
• Updated documentation CI to allow and validate the new kubernetes-platforms domain.

Why

Talos Linux and Omni were significant gaps in a 2026 infrastructure reference, particularly for immutable Kubernetes nodes, bare-metal and virtualized cluster lifecycle, Proxmox integration, secure fleet access, and multi-cluster operations.

The guides intentionally keep standalone Talos procedures separate from Omni-managed workflows so readers do not assume direct Talos administration applies unchanged after Omni takes management authority.

Validation

• Reviewed current Talos Linux 1.13 and Omni documentation from Sidero Labs.
• Based the branch on the current main, including the recently merged spec-driven development guide.
• Updated all repository links and Mermaid references alongside the new pages.
• GitHub Actions will validate Markdown structure, the new domain, Mermaid blocks, and internal links before merge.