Update project configuration and documentation

- Modified .gitignore to retain rules directory while excluding other cursor files.
- Updated backend-go.mdc to clarify compatibility notes.
- Enhanced project-conventions.mdc with guidelines on coding practices and running tests.
- Added SKILL.md for detailed instructions on running backend and frontend tests in the hnh-map monorepo.

.gitignore

@@ -23,6 +23,4 @@ frontend/dist
 
 # OS / IDE
 .DS_Store
-.cursor/*
-!.cursor/rules/
 .vscode/