fix: prevent stale Foundry CLI AUR publishes

[anandpant]

Changes

• Reject equal/older Foundry CLI version+pkgrel against cloned AUR metadata before writing, so retrying an old run cannot downgrade AUR.
• Leave other package publishing unchanged; ordinary non-force push rejects concurrent stale writes.

Checks

• Reproduced the old publisher downgrading a local fake AUR repository.
• Five real-local-git regression cases pass (older version/revision, equal, newer version/revision); full package validation and ShellCheck pass. No real AUR writes.

Completes the no-downgrade requirement in shpitdev/foundry-cli#829, following #45.