Bumps the default Gemini model across the Google ADK showcase from
gemini-2.5-flash to gemini-3.1-flash-lite — the closest GA model in
the Gemini 3.x line (2.5 family is slated for June 2026 deprecation).
Touches agent factories (DEFAULT_MODEL, _DEFAULT_A2UI_MODEL, _SUB_MODEL),
the A2UI default-model test fixture, QA docs, the manifest description
for the reasoning demo, and prose references in shared_chat docstring +
entrypoint comment.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The showcase framework directories better reflect their role as
integration examples rather than distributable packages.
Renames showcase/packages/ -> showcase/integrations/ and updates
the test docker-compose file reference accordingly.
Tyler Slaton