feat: add deploy pipeline and switch Dockerfile to COPY-based build

Add deploy_server Drone pipeline that builds and pushes the Docker image
to Gitea Container Registry, then deploys to VPS via SSH. Switch
Dockerfile from git clone to COPY-based build for CI compatibility and
better layer caching. Change exposed port to 3001.

.drone.yml

@@ -27,3 +27,46 @@ steps:
     commands:
       - npm ci
       - npm run check_format
+
+---
+
+kind: pipeline
+type: docker
+name: deploy_server
+
+steps:
+  - name: upload_to_registry
+    image: plugins/docker
+    settings:
+      registry: gitea.gilmour109.de
+      repo: gitea.gilmour109.de/Gilmour109/calchat-server
+      dockerfile: apps/server/docker/Dockerfile
+      tags:
+        - latest
+        - main
+      username:
+        from_secret: gitea_username
+      password:
+        from_secret: gitea_password
+
+  - name: ssh
+    image: appleboy/drone-ssh
+    settings:
+      host:
+        - 10.0.0.1
+      username: root
+      password:
+        from_secret: vps_ssh_password
+      envs:
+        - gitea_username
+        - gitea_password
+      port: 22
+      command_timeout: 2m
+      script:
+        - docker login -u $GITEA_USERNAME -p $GITEA_PASSWORD gitea.gilmour109.de
+        - docker pull gitea.gilmour109.de/gilmour109/calchat-server:latest
+        - docker compose -f /root/calchat-mongo/docker-compose.yml up -d
+
+depends_on:
+  - server_build_and_test
+  - check_for_formatting