Implement SemVer CLI release and Homebrew flow

[joyzoursky]

Summary

• Implement a full macOS CLI release flow for skytest-agent with SemVer tag validation, dual-architecture artifacts, and Homebrew formula generation.
• Add skytest version so packaged installs can be validated reliably by formula tests and operators.
• Document release operations and Homebrew usage for maintainers and operators.

Changes

• Reworked .github/workflows/release-cli.yml to:
  • trigger on v* tags or manual version input
  • validate and normalize SemVer (vX.Y.Z)
  • build darwin arm64 and amd64 release archives
  • generate checksums.txt
  • publish release assets to GitHub Releases
  • optionally update a Homebrew tap formula via HOMEBREW_TAP_PAT
• Updated tools/release/build-cli-macos.sh:
  • normalize architecture naming
  • produce skytest-<version>-darwin-<arch>.tar.gz
  • inject SKYTEST_CLI_VERSION into packaged launcher
• Updated tools/release/homebrew-formula-template.rb:
  • architecture-specific URLs/SHA256
  • formula test checks skytest version
  • exports SKYTEST_CLI_VERSION in installed launcher
• Added CLI support for skytest version in parser/entrypoint and parser tests.
• Added maintainer runbook docs/maintainers/cli-release-homebrew.md and linked release/install guidance from docs and README.

Validation

• Lint/type/audit: npm run verify (pass)
• CLI smoke: npm run --workspace @skytest/cli skytest -- version (prints package version)
• Release packaging smoke:
  • tools/release/build-cli-macos.sh 0.1.0 arm64 (pass)
  • tools/release/build-cli-macos.sh 0.1.0 amd64 (pass)

Breaking Changes

• Release tag convention changed from skytest-cli-v* to v* for CLI releases.
• Release asset names changed from skytest-<version>-macos-x86_64.tar.gz to skytest-<version>-darwin-{arm64|amd64}.tar.gz.

Risks

• Homebrew tap auto-update requires a valid HOMEBREW_TAP_PAT and correct HOMEBREW_TAP_REPO; misconfiguration skips/blocks tap updates.
• Workflow now matches all v* tags; non-CLI tag usage in this repo would also trigger this workflow.

Follow-ups

• Decide whether to scope tag trigger further if the repo introduces other v* release workflows.
• After merge, run a first real release (vX.Y.Z) and verify brew tap + brew install skytest end-to-end.