fix(skill): harden install.sh TTY probe and link skill from root README

- Add has_tty() helper that probes /dev/tty by actually opening it for read
  Fixes edge case where [[ -r /dev/tty ]] is true but reading fails under pipe
  redirect like < /dev/null. Mode 1 under pipe now exits 1 cleanly.
- Update root README with "Claude Code Skill" section advertising tarball +
  SHA256 install one-liner for easy discovery and installation.

Merge pull request #3 from nextlevelbuilder/feat/complete-cli-commands

feat(cli): complete command coverage for all GoClaw backend APIs

Merge pull request #1 from nextlevelbuilder/claude/agitated-shirley

feat(cli): multi-tenant support, 12 new command groups, modularization

fix(ci): pass GITHUB_TOKEN env var to goreleaser hook

feat(ci): add semantic-release for automatic versioning

Replace manual tag-based releases with go-semantic-release that
auto-creates tags from conventional commits and triggers GoReleaser.