Extract homelab-platform-blueprints + personal-stack adopt

[jorisjonkers-dev-agents]

Objective: reusable NixOS/k3s/Flux module subsets + generic bootstrap/validate scripts as a Nix flake input. Keep host data, secrets, app manifests, Nomad/Consul jobs, fleet.yaml, render outputs LOCAL.

Work:

• Identify generic module/script subset
• personal-stack consumes flake input; local-only data stays put

Part of #605.