Consolidate CI and deployment workflows

Add a deploy workflow that builds and pushes the Docker image from
the server working directory and runs docker compose on main. Trim
CI to a focused Node build in an alpine container (apk deps,
npm ci, npm run build) and remove the old docker workflow. Simplify
Dockerfile to a builder+runtime flow (npm ci, npm prune,
copy node_modules) and make docker-compose use the registry image
and proxy network.

docker-compose.yml

@@ -1,10 +1,12 @@
 services:
   cozy-den:
-    build: .
+    image: git.hiddenden.cafe/hiddenden/cozy-den:latest
     container_name: cozy-den
-    ports:
-      - "3000:3000"
+    # ports:
+    #   - "3000:3000"
     restart: unless-stopped
+    networks:
+      - proxy
     environment:
       - NODE_ENV=production
       - HOST=0.0.0.0
@@ -18,3 +20,7 @@ services:
 
 volumes:
   guestbook_data:
+
+networks:
+  proxy:
+    external: true