Fix(docker) : Update Dockerfile and docs to use Poetry and NPM

[allamiro]

Motivation and Context

The Docker production build currently fails on the master branch because the Dockerfile expects legacy dependency files (requirements/ and yarn.lock) that have been migrated to Poetry and modern NPM. This PR updates the Docker setup to align with the current architecture of the repository.
Closes #1699

What has changed

• Dockerfile Base Images: Updated Node from 8 to 18 and Python from 3.6 to 3.12 to prevent EOL build failures and align with current project requirements.
• Frontend Build: Migrated from yarn to npm ci using package-lock.json.
• Backend Build: Replaced pip install -r requirements.txt with poetry install, directly utilizing pyproject.toml and poetry.lock. Implemented conditional logic to exclude dev dependencies in production builds.
• .dockerignore: Cleaned up legacy file references and added modern ignore rules (.venv, poetry.toml, etc.) to optimize the build context.
• Documentation: Updated docs/prodinstalldocker.rst to replace deprecated docker-compose commands with the modern docker compose plugin syntax.

Testing

• Verified that the Docker image builds successfully locally without looking for missing requirement files.
• Confirmed the multi-stage build correctly passes the compiled frontend assets and translations to the final image.

[allamiro]

Rebased on the latest master. The PR updates the Docker build to match the current repository state (pyproject.toml/poetry.lock and package-lock.json) and removes reliance on legacy requirements/ and yarn.lock.

[edward-ly]

@allamiro Thanks so much for taking care of this! Before we merge this, do you mind if we ask what you plan to do with the Docker container?

[allamiro]

@allamiro Thanks so much for taking care of this! Before we merge this, do you mind if we ask what you plan to do with the Docker container?

Thanks for asking! The plan is to use this container to support a self-hosted, air-gapped Kubernetes environment for our Nextcloud instances. Because we support teams across multiple locations using static, IP-based infrastructure, this image provides the foundation for a portable, isolated deployment. While I am still finalizing the strategy for offline dependency management and internal image and apps mirroring, this PR establishes the core build logic required for our internal hosting workflow. Working on the feature and the documentation. If you have any feedback or additional information that i need to add please let me know
https://github.com/allamiro/appstore/tree/docs/airgapped-install-guide
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