Rename basic catalog scaffolding examples for better clarity

As discussed in PR #1497 (https://github.com/a2ui-project/a2ui/pull/1497#discussion_r3416520470), the `00_` prefix on some basic catalog examples (e.g., `00_capitalized-text.json`) was used as a trick to sort them first.

To make their purpose more explicit and to make it easier to filter them out in public gallery applications (where they might not give a good impression of A2UI's capabilities if shown at the top), we should clearly label them as examples used to scaffold an app.

Suggested renaming:
- `00_capitalized-text.json` -> `scaffold_00_capitalized-text.json`
- `00_complex-layout.json` -> `scaffold_01_complex-layout.json`
- etc., or follow the numbering scheme used elsewhere so they are consistent.

Find the basic catalog scaffolding examples in the repository, likely in a directory like 'examples' or 'catalog'. Rename the files from '00_capitalized-text.json' to 'scaffold_00_capitalized-text.json' and similarly for others, maintaining the numbering scheme. Verify that any references to these files in documentation or code are updated, and ensure the changes do not break existing functionality.

Written by the indexing model from the issue text.