chore: add Arch PKGBUILD for Handy release packaging

[Kreijstal]

Before Submitting This PR

• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate
• I have read CONTRIBUTING.md

If this is a feature or change that was previously closed/rejected:

• I have explained in the description below why this should be reconsidered
• I have gathered community feedback (link to discussion below)

Human Written Description

I added a repository-native Arch Linux packaging path so users can install Handy using a standard makepkg/Pacman workflow without manual extraction steps. This makes it easier for Arch users to install and keep the app in a package-managed way.

The change keeps binaries and resources as shipped in the upstream release .deb and stages the same layout under /usr, which matches the existing runtime expectations of the app.

Related Issues/Discussions

Fixes #
Discussion:

Community Feedback

None yet.

Testing

• Built a local PKGBUILD-based package with makepkg
• Installed the package and verified the app entry point runs: handy --help

Screenshots/Videos (if applicable)

Not applicable (packaging change only).

AI Assistance

• No AI was used in this PR
• AI was used (please describe below)

Tools used:

• ChatGPT/Codex for workflow and patch scaffolding, shell verification, and packaging checks

How extensively:

• Drafted PKGBUILD and validated build/install flow end-to-end