feat: Add optimized build profile and Debian packaging for ARMv6

[tomoyan596]

Summary

This PR introduces a dedicated build profile and Debian packaging setup to support low-resource devices, specifically tested on Raspberry Pi Zero WH (ARMv6).

Key Changes

• New Cargo Profile (dietpi): Optimized for binary size (opt-level = 'z', LTO, strip = true). Reduces the server binary size from ~66MB to ~45MB (-31%).
• Debian Packaging: Added package.metadata.deb configuration for both atomic-server and atomic-cli.
• Cross-build Support: Updated Cross.toml for Node.js/pnpm environments.
• Systemd Integration: Included a service unit and an environment file (/etc/atomic-server/atomic-server.env) for professional service management.
• Security: The server now runs under a dedicated atomic-server system user (created via postinst).
• Dynamic Configuration: The postinst script automatically sets ATOMIC_DOMAIN to the system's hostname upon installation.

Motivation

Standard release builds are somewhat heavy for older SBCs with limited RAM (e.g., 512MB). This PR makes Atomic Data more accessible for edge computing and lightweight server use cases.
Related to #151.

Verified on: Fedora 42 (Cross-build) -> DietPi (Raspberry Pi Zero WH)
The instructions are written in Japanese, but more detailed information is available on the following website, so please refer to it if you wish.
https://www.tomoyan.net/rust/cross-compilation_for_dietpi

[joepio]

No this is not how copyright works :P I wrote pretty much the entire repo, you can't claim ownership with one PR that adds some metadata.

[joepio]

Hey @tomoyan596 thanks for the PR! Looks like this helps in making it more accessible indeed. And while I do want to credit you where credit is due, I don't think it makes sense for you to be listed as copyright owner & maintainer ;)

[tomoyan596]

Hi @joepio,

My apologies for the metadata blunder—I've just pushed a fix!

• Metadata: Updated the maintainer and copyright to your official info (joep@ontola.io) across all packages.

• Systemd Service: Cleaned up the service unit by moving all environment variables to the .env file for better consistency.

I've re-tested the Debian package on a Raspberry Pi Zero WH (DietPi), and it's working perfectly. Thanks for the feedback!

[tomoyan596]

I noticed atomic-cli was missing the homepage field, so I added it to keep the Debian metadata consistent with atomic-server.