Demo UI fails to run due to pypika build failure

### What happened?

### Steps to reproduce
1. Clone `a2a-samples`
2. Follow instructions in Demo's `README.md`
3. `uv run main.py` fails with the log output below

### Environment config
```
==> sw_vers
ProductName: macOS
ProductVersion: 26.0.1
BuildVersion: 25A362

==> python3 --version
Python 3.14.0

==> uv --version
uv 0.9.2 (141369ce7 2025-10-10)
```

### Relevant log output

```shell
==> uv run main.py
Using CPython 3.14.0 interpreter at: /opt/homebrew/opt/python@3.14/bin/python3.14
Creating virtual environment at: /Users/dmt/Dev/a2a-samples/.venv
× Failed to build `pypika==0.48.9`
├─▶ The build backend returned an error
╰─▶ Call to `setuptools.build_meta:__legacy__.build_wheel` failed (exit status: 1)

[stderr]
Traceback (most recent call last):
File "", line 14, in
requires = get_requires_for_build({})
File "/Users/dmt/.cache/uv/builds-v0/.tmpw28aR2/lib/python3.14/site-packages/setuptools/build_meta.py", line
331, in get_requires_for_build_wheel
return self._get_build_requires(config_settings, requirements=[])
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/dmt/.cache/uv/builds-v0/.tmpw28aR2/lib/python3.14/site-packages/setuptools/build_meta.py", line
301, in _get_build_requires
self.run_setup()
~~~~~~~~~~~~~~^^
File "/Users/dmt/.cache/uv/builds-v0/.tmpw28aR2/lib/python3.14/site-packages/setuptools/build_meta.py", line
512, in run_setup
super().run_setup(setup_script=setup_script)
~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/dmt/.cache/uv/builds-v0/.tmpw28aR2/lib/python3.14/site-packages/setuptools/build_meta.py", line
317, in run_setup
exec(code, locals())
~~~~^^^^^^^^^^^^^^^^
File "", line 38, in
File "", line 20, in version
AttributeError: module 'ast' has no attribute 'Str'

hint: This usually indicates a problem with the package or the build environment.
help: `pypika` (v0.48.9) was included because `a2a-samples-image-gen` (v0.1.0) depends on `crewai>=0.95.0` (v0.95.0)
which depends on `chromadb>=1.1.0, <1.2.dev0` (v1.1.1) which depends on `pypika>=0.48.9`
```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The issue is a build failure for pypika 0.48.9 with Python 3.14, due to an AttributeError about `ast.Str`. Check the project's dependency chain: `crewai>=0.95.0` -> `chromadb>=1.1.0, <1.2.dev0` -> `pypika>=0.48.9`. Look at the `pyproject.toml` or `requirements.txt` in the a2a-samples repository. Investigate if pypika has a newer version compatible with Python 3.14, or if a dependency constraint needs to be updated. Running `uv run main.py` reproduces the error.

Rédigé par le modèle d'indexation à partir du texte de l'issue.