build: remove Nix flakes — Guix-only build policy (#260)

Estate-wide Guix-only policy (owner ruling 2026-06-05): removes 7 flake
files (root + echidnabot + sustainabot) and reconciles functional
references (Justfile RSR checks, skeleton dev-shell, CONTRIBUTING,
echidnabot compliance docs) to guix.scm.

https://claude.ai/code/session_016R5WsMHtpnD8bmrkjFNFmg

Author: hyperpolymath

CONTRIBUTING.md

@@ -2,8 +2,8 @@
 git clone https://github.com/hyperpolymath/gitbot-fleet.git
 cd gitbot-fleet
 
-# Using Nix (recommended for reproducibility)
-nix develop
+# Using Guix (recommended for reproducibility)
+guix shell -D -f guix.scm
 
 # Or using toolbox/distrobox
 toolbox create gitbot-fleet-dev
@@ -41,7 +41,7 @@ gitbot-fleet/
 ├── MAINTAINERS.md
 ├── README.adoc
 ├── SECURITY.md
-├── flake.nix            # Nix flake (Perimeter 1)
+├── guix.scm             # Guix manifest (Perimeter 1)
 └── Justfile             # Task runner (Perimeter 1)
 ```
 

bots/echidnabot/RELEASE_CHECKLIST.md

@@ -140,7 +140,6 @@ Complete checklist for making echidnabot a perfect release.
 - [x] Justfile for task automation
 
 ### To Add
-- [ ] flake.nix for Nix users
 - [ ] cargo-deb configuration
 - [ ] cargo-rpm configuration
 - [ ] Homebrew formula (optional)

bots/echidnabot/RSR_COMPLIANCE.adoc

@@ -55,7 +55,7 @@ This document describes the Rhodium Standard Repository (RSR) compliance status
 |LICENSE.txt (AGPL + Palimpsest) |✓ |MPL-2.0
 |Containerfile present |✓ |Multi-stage build with Chainguard base
 |guix.scm present |✓ |Guix package definition (primary)
-|flake.nix present |✗ |TODO: Add Nix flake (fallback)
+|Nix flake (flake.nix) |N/A |Removed 2026-06-05 — Guix-only policy (guix.scm above)
 |===
 
 == Security Compliance
@@ -80,7 +80,6 @@ None
 == Action Items
 
 * [ ] Add Justfile for task running
-* [ ] Add flake.nix for Nix users (fallback package manager)
 
 == References
 

bots/echidnabot/flake.lock

@@ -113,8 +113,8 @@ validate-rsr:
     for f in .well-known/security.txt .well-known/ai.txt .well-known/humans.txt; do
         [ -f "$f" ] || MISSING="$MISSING $f"
     done
-    if [ ! -f "guix.scm" ] && [ ! -f ".guix-channel" ] && [ ! -f "flake.nix" ]; then
-        MISSING="$MISSING guix.scm/flake.nix"
+    if [ ! -f "guix.scm" ] && [ ! -f ".guix-channel" ]; then
+        MISSING="$MISSING guix.scm"
     fi
     if [ -n "$MISSING" ]; then
         echo "MISSING:$MISSING"