ci(release): publish Homebrew tap formula on tagged releases

[jamiesun]

Summary

Adds a Homebrew distribution channel for sshx, mirroring the pattern used in talkincode/scoot's release workflow.

• New opt-in homebrew job in .github/workflows/release.yml, running after build on tag pushes.
  • Gated on the HOMEBREW_TAP_TOKEN secret; without it the job's steps are skipped and the rest of the release is unaffected.
  • Reads checksums.txt from the build artifacts, clones talkincode/homebrew-tap, and renders Formula/sshx.rb covering darwin/linux on amd64/arm64 (Windows has no Homebrew equivalent).
  • Commits and pushes only when the formula content actually changes.
• Documented the new brew install talkincode/tap/sshx install path in README.md / README_CN.md.
• Added a "Homebrew Tap Publishing" section to RELEASE.md with one-time setup steps (create tap repo, PAT, HOMEBREW_TAP_TOKEN secret) and verification instructions.
• Updated AGENT.md §11 and docs/roadmap.md to reflect the new install path/capability.
• Added a CHANGELOG.md [Unreleased] entry.

Setup required before this is live

HOMEBREW_TAP_TOKEN (a fine-grained PAT scoped to Contents: write on a talkincode/homebrew-tap repo) needs to be added as a repository secret. Until then, the job safely no-ops.

Bugfix reflection

Not applicable — this is a new capability (release automation), not a bug fix.

Verification run

• python3 -c "import yaml; yaml.safe_load(open('.github/workflows/release.yml'))" — workflow YAML parses.
• ruby -c against a rendered sample formula — valid Ruby/Homebrew DSL syntax.
• Simulated the checksums.txt sha-lookup shell logic locally — correct hash extraction and correct hard failure on a missing checksum.
• actionlint .github/workflows/release.yml — all reported findings are pre-existing (unrelated lines), nothing flagged in the new homebrew job.
• make check (fmt, vet, test) — all pass, unaffected since no Go code changed.
• Pre-commit/pre-push hooks (gofmt, go vet, full test suite with coverage) ran clean.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com