fix: resolve GBK encoding errors on Windows for Chinese content

[Mars-ending]

Problem

On Windows systems with Chinese locale, Python's stdout uses GBK encoding by default. This causes UnicodeEncodeError when:

1. Model responses contain CJK characters or emoji
2. Logs are written to files via FileHandler without encoding specified

Error example:
'gbk' codec can't encode character '\U0001f4d6' in position 1189

Changes

1. server_main.py:

   • Wrap sys.stdout/stderr with UTF-8 TextIOWrapper on Windows
   • Add encoding='utf-8' to FileHandler for server.log

2. utils/structured_logger.py:

   • Add encoding='utf-8' to FileHandler for workflow logs

3. utils/logger.py:

   • Wrap print() in try/except for UnicodeEncodeError fallback
   • On encoding error, strip problematic characters gracefully

Testing

Verified on Windows 11 with Chinese locale:

• Workflow with Chinese task prompts now completes without encoding errors
• Generated files correctly contain Unicode characters (CJK, emoji)

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