refactor: rename a2ui prefixed json schemas and update references

[jacobsimionato]

Description of Changes

This pull request removes the redundant a2ui_ prefix from the client-related JSON schemas:

• a2ui_client_capabilities.json is renamed to client_capabilities.json.
• a2ui_client_data_model.json is renamed to client_data_model.json.

Corresponding schema ids ($id) and markdown document references across v0_9 and v0_10 specifications, as well as the catalogs.md concept guide, have been updated to reflect these new file names.

Rationale

The a2ui_ prefix is redundant within the context of the A2UI repository. Removing it improves consistency and simplifies the naming conventions for schemas.

Testing/Running Instructions

• Review the changed references in the documentation and schemas.
• Ensure that tools relying on schema validation still pass without missing file errors. You can run validation locally if needed using the validation scripts.

[gemini-code-assist]

Code Review

This pull request refactors the project by renaming two client-related JSON schema files, a2ui_client_capabilities.json and a2ui_client_data_model.json, removing the a2ui_ prefix to improve naming consistency. All corresponding references in the documentation and schema $id fields across both v0_9 and v0_10 specifications have been updated accordingly. The changes appear to be consistent and correctly implemented as described.