chore: release pipeline follow-up — AUR PKGBUILD + Homebrew tap

[chmmou]

Follow-up to #81. Once the base release pipeline (binaries + deb/rpm + cosign) is stable, extend distribution coverage:

Scope

• AUR: goreleaser aurs: section pushing PKGBUILD to a separate kasapi-cli-bin (or kasapi-cli) repo on AUR. Requires AUR account + SSH key in repo secrets.
• Homebrew tap: goreleaser brews: section publishing a formula to a homebrew-tap repo under the same org. Requires the tap repo + a GITHUB_TOKEN with write access to it.

Out of scope

• AppImage — overkill for a static Go binary; tarball + deb/rpm cover Linux distribution.

Notes

Defer until there is real demand on either channel, since each adds an external repo to maintain.