Add version indicator/toggle to A2UI Composer basic catalog

[nilkrdg]

Currently, the basic catalog (/basic-catalog) displays the updated v0.9 component shapes (like the flattened MultiChoice properties), but there is no visual indicator or toggle on the page showing which specification version is currently active.

Link to the basic catalog:
https://a2ui-composer.ag-ui.com/basic-catalog

Since v0.8 is the stable production version and v0.9 introduces structural changes, missing a version badge causes confusion when tracking schema mismatches. Please add a clear version label or selector to the UI.

[nilkrdg]

Are there plans to drop support for v0.8 of A2UI? Currently, users cannot view the v0.8 components in the official basic catalog document, which defaults to v0.9 shapes. Clarification on the support lifecycle for v0.8 would be very helpful.