ci: target this instance's nix runner

- run on the 'nix' label with Nix preinstalled; drop the installer action
- replace the inline release API calls with vpm/publish.sh
- add curl to the devShell for the publish step

vpm/publish.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Creates the Gitea release for the current tag and attaches the VPM zip built by package.sh.
+#
+# Needs `curl` and `jq`: run it inside `nix develop`.
+#
+# Environment:
+#   TOKEN   required, Gitea token with repository write access
+#   SERVER  required, e.g. https://git.scug.io
+#   REPO    required, e.g. doloro/av3-animation-as-crab
+#   TAG     required, release tag
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")/.." && pwd)
+manifest="$root/csharp/dev.doloro.animator-as-crab/package.json"
+
+id=$(jq -r .name "$manifest")
+version=$(jq -r .version "$manifest")
+zip="$root/vpm/dist/$id-$version.zip"
+
+zip_name=$(basename "$zip")
+[ -f "$zip" ] || { echo "missing $zip; run package.sh first" >&2; exit 1; }
+
+release=$(curl -fsS -X POST \
+  -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
+  "$SERVER/api/v1/repos/$REPO/releases" \
+  -d "$(jq -n --arg tag "$TAG" --arg name "$id $version" '{tag_name: $tag, name: $name}')")
+
+asset_url="$SERVER/api/v1/repos/$REPO/releases/$(jq -r .id <<<"$release")/assets?name=$zip_name"
+
+curl -fsS -X POST \
+  -H "Authorization: token $TOKEN" \
+  "$asset_url" \
+  -F "attachment=@$zip"
+
+echo "released $TAG with $zip_name"