[fix] set encoding to utf-8 in samples' tool.py while open sample data file

[zhujie2006]

##Problem##
The A2UI sample running in a Windows shell can get this, while using a different codec

##Solution##
Set the encoding parameter while opening the xxx_data.json file

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[triceviola24-sys]

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[bckim9489]

Thanks for the fix - this resolves the Windows UnicodeDecodeError nicely 👍

I was able to reproduce the original issue on Windows 11 (Python + uv):
UnicodeDecodeError: 'cp949' codec can't decode ... when reading restaurant_data.json.

With this change (encoding="utf-8"), the sample agent starts successfully and the demo flow works end-to-end on Windows.

As a small, optional follow-up idea (non-blocking):
would you consider using pathlib for building the file path and reading the data?
It can slightly improve readability and keep the path handling fully platform-independent.

For example:

from pathlib import Path

file_path = Path(__file__).with_name("restaurant_data.json")
restaurant_data_str = file_path.read_text(encoding="utf-8")

Totally optional - the current fix already solves the problem well.
Just wanted to share this as a possible improvement.