Initial commit: FastGPT Python SDK Phase 1

Implement core infrastructure:

- BaseClientMixin with retry logic and validation
- FastGPTClient base class with httpx
- ChatClient with 11 chat operation methods
- AppClient for analytics and logs
- Custom exceptions (APIError, AuthenticationError, etc.)
- Package configuration (pyproject.toml, setup.py)
- Documentation (README.md, CLAUDE.md)
- Basic usage examples

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

setup.py

@@ -0,0 +1,5 @@
+"""Setup configuration for fastgpt-client."""
+
+from setuptools import setup
+
+setup()