[Post-redesign] Improve widget library

As a user, I want to **select a widget from an improved widget library**, so that I can quickly add relevant visualizations to my dashboard without starting from scratch.
- The library is organized into categories (e.g., Frontend, Backend, Web Vitals) to help users find widgets relevant to their use case.
- Each widget in the library includes a name, a description of the data and visualization, and a preview option.
- Users can search for specific widgets using a search bar for easier discovery.
- Selected widgets can be directly added to the dashboard or previewed and customized before finalizing.

Not final mock: