Re-enable AUR publishing in release workflow (SSH key passphrase issue)

[vriesdemichael]

Summary

The aur-release job was removed from .github/workflows/release.yml because it failed on every release, blocking nothing downstream but producing a red release run each time.

Failure

KSXGitHub/github-actions-deploy-aur@v4.1.3 cannot load the deploy key:

Importing private key
  mode of '/home/builder/.ssh/aur' changed from 0644 to 0600
  debug1: read_passphrase: stdin is not a tty
  Enter passphrase for "/home/builder/.ssh/aur": Load key "/home/builder/.ssh/aur": incorrect passphrase supplied to decrypt private key

The AUR_KEY secret is a passphrase-protected SSH private key. The action feeds the key to ssh non-interactively and has no way to supply a passphrase, so the key fails to decrypt and the publish aborts.

Fix to re-enable

One of:

1. Replace the AUR_KEY secret with a passphrase-less SSH private key dedicated to AUR deployment (regenerate with ssh-keygen -t ed25519 -N "" ..., register the public key on the AUR account), or
2. Switch to an action/approach that supports an encrypted key + passphrase.

Then restore the aur-release job (see the removal commit / PR for the exact block). The PKGBUILD generator scripts/gen_pkgbuild.py was left in place for reuse.

Context

Removed as part of getting the release pipeline green again, alongside the nfpm ${PKG_BINARY} expansion fix (#251).