chore(nix->guix): remove flake.nix (Guix-only) (#275) #508

Job	Run time
governance / Well-Known (RFC 9116 + RSR)	8s
governance / Workflow security linter	4s
governance / Guix primary / Nix fallback policy	6s
governance / Validate Hypatia baseline	6s
governance / Language / package anti-pattern policy	13s
governance / Security policy checks	4s
governance / Licence consistency	10s
governance / Code quality + docs	21s
governance / Trusted-base reduction policy	7s
	1m 19s

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