Add NUR export validation script

tasks/validate-nur

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -Eeuo pipefail
+
+for channel in 'unstable' 'nixpkgs'; do
+  nix_args=(
+    --option restrict-eval 'true'
+    -I './'
+    -I "$channel=$(realpath "$(nix-instantiate --find-file "$channel")")"
+    --arg 'pkgs' "import <$channel> { overlays = [ ]; }"
+  )
+
+  nix-env "${nix_args[@]}" --file 'nur.nix' --query '*' --available --meta --json \
+  | jq --raw-output 'to_entries[] | "\(.key)\(.value.meta.broken)"' \
+  | while IFS='' read -r name broken; do
+    if [[ $broken == 'true' ]]; then
+      echo "⚠️ Build marked as broken for $name@$channel"
+    elif nix-build "${nix_args[@]}" 'nur.nix' --attr "$name" --no-out-link; then
+      echo "✅ Build succeeded for $name@$channel"
+    else
+      echo "❌️ Build failed for $name@$channel"
+    fi
+  done
+done