Add verified Stack Homebrew formula

[konojunya]

Summary

• add the official stack-sh/tap/stack formula for Stack CLI 0.3.0
• map Apple Silicon macOS and ARM64/x86_64 Linux to the exact GitHub Release archives and digests
• verify all referenced archives against the release manifest, checksum inventory, provenance, SBOM attestations, signer workflow, tag ref, and GitHub-hosted runners before formula updates
• test install, representative CLI commands, formula-revision upgrade, uninstall, and preservation of XDG configuration and icon data
• document supported hosts, trust scope, maintenance, rollback, and private vulnerability reporting

The Intel macOS archive is verified and retained only so Homebrew can load the formula before reporting its ARM64 requirement; Intel macOS remains unsupported by this formula.

Validation

• scripts/test-formula-source.sh
• scripts/update-stack-formula.sh 0.3.0
• brew style stack-sh/tap
• brew audit --strict --os all --arch all stack-sh/tap/stack
• brew livecheck stack-sh/tap/stack
• scripts/test-formula-lifecycle.sh stack-sh/tap on Apple Silicon macOS
• actionlint .github/workflows/ci.yaml
• shellcheck --shell=bash --enable=all scripts/*.sh
• git diff --check