chore: update project license from MIT to GPLv3 in README and package.json

Author: Coderrob

README.md

@@ -365,7 +365,7 @@ We welcome contributions! Please see our contribution guidelines and ensure all
 
 ## License
 
-This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+This project is licensed under the GPLv3 License - see the [LICENSE](LICENSE) file for details.
 
 ## Support & Documentation
 

package.json

@@ -61,6 +61,7 @@
     "LICENSE",
     "CHANGELOG.md"
   ],
+  "license": "GPL-3.0",
   "main": "dist/index.cjs",
   "module": "dist/index.mjs",
   "name": "@coderrob/backstage-mcp-server",