Knowledge Explorer Step 15: Rearrange and Contain

Reorganize the project by feature. Everything belonging to search goes in one folder; everything genuinely shared goes in another, and be strict about what qualifies. Then add an error boundary around the application and a second around the results area, and prove both work by deliberately throwing inside a component. The application should degrade to a useful message rather than a blank page. Delete anything left over from the reorganization, including the state switcher from module 7 if the real request now covers every path.