Fix base image: use mirror direct path, switch to node:20-alpine

Mirror exposes images as mirror.soroushasadi.com/<image> directly,
not via /repository/docker-group/ path. Also node:20-alpine is already
cached on the server; node:20-slim was never pulled.

Dockerfile: apk instead of apt-get, addgroup/adduser instead of
groupadd/useradd (Alpine BusyBox compatibility).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
 
       - name: Docker Build Test
         env:
-          NODE_IMAGE: mirror.soroushasadi.com/repository/docker-group/node:20-slim
+          NODE_IMAGE: mirror.soroushasadi.com/node:20-alpine
           NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
         run: |
           docker build \

.gitea/workflows/deploy.yml

@@ -41,7 +41,7 @@ jobs:
 
       - name: Build Container
         env:
-          NODE_IMAGE: mirror.soroushasadi.com/repository/docker-group/node:20-slim
+          NODE_IMAGE: mirror.soroushasadi.com/node:20-alpine
         run: |
           docker compose build