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.
Add Drone CI with server build/test and format check pipelines.
Add unit tests for password utils and recurrenceExpander.
Add check_format script, fix Jest config to ignore dist/,
remove dead CaldavService.test.ts, apply Prettier formatting.
