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/package.json

@@ -0,0 +1,51 @@
+{
+  "name": "@gastown/gt",
+  "version": "0.1.0",
+  "description": "Gas Town CLI - multi-agent workspace manager with native binary support",
+  "main": "bin/gt.js",
+  "bin": {
+    "gt": "bin/gt.js"
+  },
+  "scripts": {
+    "postinstall": "node scripts/postinstall.js",
+    "test": "node scripts/test.js"
+  },
+  "keywords": [
+    "multi-agent",
+    "workspace-manager",
+    "ai-agent",
+    "coding-agent",
+    "claude",
+    "git",
+    "orchestration"
+  ],
+  "author": "Steve Yegge",
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/steveyegge/gastown.git",
+    "directory": "npm-package"
+  },
+  "bugs": {
+    "url": "https://github.com/steveyegge/gastown/issues"
+  },
+  "homepage": "https://github.com/steveyegge/gastown#readme",
+  "engines": {
+    "node": ">=14.0.0"
+  },
+  "os": [
+    "darwin",
+    "linux",
+    "win32"
+  ],
+  "cpu": [
+    "x64",
+    "arm64"
+  ],
+  "files": [
+    "bin/",
+    "scripts/",
+    "README.md",
+    "LICENSE"
+  ]
+}