Expand GoReleaser configuration for archives and Homebrew tap publishing

[takai]

This pull request extends the GoReleaser setup to cover additional release targets and to make the release behavior more explicit.

Key changes:

• Refined archive configuration

  • Use tar.gz as the default archive format
  • Generate zip archives for macOS builds via format_overrides

• Added Homebrew tap publishing

  • Automatically generate and commit a Formula to takai/homebrew-tap
  • Configure metadata such as homepage, description, license, and install steps
  • Use an environment token for authenticated pushes

• Restructured GoReleaser YAML

  • Expanded sections (builds, archives, checksum, changelog) for clarity
  • No functional changes to existing build settings beyond the items above

These changes improve release automation and make it easier for users to install and verify git-ai-commit across platforms.