refactor: implement script tag approach for library inclusion

- Add script tags to demo-site HTML files for manual development
- Disable CLI inline script injection to prevent duplicate scripts
- Add library serving endpoints to servedev command
- Update build process to auto-copy library to demo-site
- Add CDN URL helpers for future production deployment
- Update .gitignore for generated demo-site files

Fixes .insertr-gate authentication for manual npm run serve workflow
while maintaining clean separation between CLI and manual setups.

lib/package.json

@@ -10,7 +10,9 @@
     "src/"
   ],
   "scripts": {
-    "build": "rollup -c",
+    "build": "rollup -c && npm run copy:demo",
+    "build:only": "rollup -c",
+    "copy:demo": "cp dist/insertr.js ../demo-site/insertr.js",
     "watch": "rollup -c -w",
     "dev": "rollup -c -w",
     "serve": "node scripts/dev.js serve",