node compatibility + npm publish prep
Replace all Bun-specific APIs in runtime code with node equivalents:
- Bun.serve() → node:http createServer (login.js OAuth callback)
- Bun.spawn() → child_process.spawn (login.js browser open)
- Bun.which() → execFileSync which helper (setup.js, adopt.js)
- Bun.spawnSync() → child_process.spawnSync (setup.js skill install)
- Shebang changed from #!/usr/bin/env bun to #!/usr/bin/env node
Add engines field (node >=20), package-lock.json, CI workflow
(bun test + node smoke tests on 20/22), and npx install docs.
Also includes vit branding (mark/brand prefix on CLI output).
153 tests pass under bun, CLI verified working under node 22.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>