fix: use apk for alpine runner

.gitea/workflows/build.yml

@@ -11,10 +11,9 @@ jobs:
   build:
     runs-on: self-hosted
     steps:
-      - name: Install build tools (apt)
+      - name: Install build tools
         run: |
-          apt-get update
+          apk add --no-cache curl git nodejs npm docker-cli 2>/dev/null || true
-          apt-get install -y curl git nodejs npm docker.io 2>/dev/null || true
 
       - name: Generate demo content + Dockerfile
         run: |