feat: Add GitHub deployment artifacts (homebrew, npm) (gt-ufep6)

- Add .goreleaser.yml for multi-platform binary releases
- Add npm-package/ with postinstall binary download
- Add release.yml workflow for GoReleaser + npm publish + Homebrew tap

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

npm-package/.npmignore

@@ -0,0 +1,12 @@
+# Ignore test files
+test/
+
+# Ignore development files
+*.md
+!README.md
+
+# Ignore any local binaries (downloaded at install time)
+bin/gt
+bin/gt.exe
+bin/*.tar.gz
+bin/*.zip