chore(skeleton): stop propagating Nix to new repos

The skeleton template is inherited by new repos, so a flake reference there
re-introduces Nix estate-wide. Drops flake.nix/flake.lock from the skeleton's
.gitignore/.gitattributes/PLAYBOOK and points CONTRIBUTING.adoc dev setup at
guix shell.

https://claude.ai/code/session_016R5WsMHtpnD8bmrkjFNFmg

Author: claude

robot-repo-automaton/CONTRIBUTING.adoc

@@ -3,8 +3,8 @@
 git clone https://github.com/hyperpolymath/robot-repo-automaton.git
 cd robot-repo-automaton
 
-= Using Nix (recommended for reproducibility)
-nix develop
+= Using Guix (recommended for reproducibility)
+guix shell -D -f guix.scm
 
 = Or using toolbox/distrobox
 toolbox create robot-repo-automaton-dev
@@ -43,7 +43,7 @@ robot-repo-automaton/
 ├── MAINTAINERS.md
 ├── README.adoc
 ├── SECURITY.md
-├── flake.nix            # Nix flake (Perimeter 1)
+├── guix.scm             # Guix manifest (Perimeter 1)
 └── Justfile             # Task runner (Perimeter 1)
 [listing]
 ----

robot-repo-automaton/templates/skeleton/.gitattributes

@@ -65,4 +65,3 @@ Containerfile  text eol=lf
 
 # Lock files
 Cargo.lock  text eol=lf -diff
-flake.lock  text eol=lf -diff

robot-repo-automaton/templates/skeleton/.gitignore

@@ -69,12 +69,6 @@ __pycache__/
 /obj/
 /bin/
 
-# Nix
-# flake.lock is ignored in the template repo because each project should
-# generate its own lock file on first use. In derived projects, REMOVE this
-# line and track flake.lock for reproducible builds.
-flake.lock
-
 # Haskell
 /.stack-work/
 /dist-newstyle/
@@ -131,7 +125,7 @@ build/
 dist/
 
 # /build/ is a tracked config directory (build orchestration: contractile.just,
-# flake.nix, just/*.just, etc.) introduced in chore/root-cleanup. Whitelist
+# guix.scm, just/*.just, etc.) introduced in chore/root-cleanup. Whitelist
 # root-level /build/ so its contents are tracked. The blanket `build/` rule
 # above still ignores any nested `build/` directories (e.g. Rust crate
 # target/build/) — only the root-level path is exempt.

robot-repo-automaton/templates/skeleton/.machine_readable/6a2/PLAYBOOK.a2ml

@@ -63,7 +63,7 @@ enforcement-workflow = ".github/workflows/estate-rules.yml"
 # .github/             CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, workflows/
 # .machine_readable/   AI manifests (0.1-AI-MANIFEST.a2ml), 6a2/ checkpoints,
 #                      contractiles/, configs/, anchors/, policies/, scripts/, svc/
-# build/               contractile.just, flake.nix, guix.scm, Containerfile,
+# build/               contractile.just, guix.scm, Containerfile,
 #                      just/*.just (Justfile section imports)
 # docs/                onboarding/, status/, architecture/, governance/  (all .adoc)
 # session/             dispatch.sh, custom-checks.k9, local-hooks.sh