Split docker-compose into production (pull) and dev (build) files

docker-compose.yml now pulls the pre-built image from
gitea.labsconnect.se/bobban/scheduletaskmanager-schedule-task-manager:latest
instead of building locally; the old build-from-source file moves to
docker-compose.dev.yml for local testing or before a push pipeline
exists. README documents both paths.

docker-compose.dev.yml

@@ -0,0 +1,14 @@
+services:
+  schedule-task-manager:
+    build: .
+    container_name: schedule-task-manager
+    restart: unless-stopped
+    ports:
+      - "${HOST_PORT:-3000}:3000"
+    env_file:
+      - .env
+    environment:
+      PORT: 3000
+      NODE_ENV: production
+    volumes:
+      - ./data:/app/data