refactor: optimize Docker image size

- Combine RUN commands to reduce layers
- Add --no-install-recommends and clean apt cache
- Use COPY --chown to set ownership during copy
- Update .dockerignore to exclude dev files and build configs

Saves ~260MB (21%) in image size
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f