Rename image variants from spin-only/spin-tailscale to compute/gateway

[kingdonb]

🏷️ Image Naming Alignment with ADR-004

Problem

Our current image names (spin-only / spin-tailscale) don't clearly communicate their architectural roles documented in ADR-004. The role-based naming would be clearer for users.

Proposed Changes

Current Names → Proposed Names:

• talos-cozystack-spin-only → talos-cozystack-compute
• talos-cozystack-spin-tailscale → talos-cozystack-gateway

Benefits

• Role clarity: Names communicate function (compute vs. gateway)
• ADR alignment: Matches ADR-004 role-based architecture documentation
• User experience: Easier to understand which image to use for which node type

Implementation Areas

• GitHub workflow matrix strategy (.github/workflows/build-talos-images.yml)
• Repository names in GitHub Container Registry
• Documentation references (README.md, index.md, ADRs)
• Test suite image references
• Any hardcoded image pulls in guides

Priority

Before December 4, 2025 (CozySummit Virtual demo)

Context

ADR-004 documents the role-based architecture discovered through real-world cluster formation issues. The naming should reflect the architectural reality rather than implementation details.