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>

.gitignore

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+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+pip-wheel-metadata/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+PIPFILE.lock
+
+# PyInstaller
+*.manifest
+*.spec
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# IDEs
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Project specific
+*.log
+*.db
+*.sqlite
+
+# Python
+.pytest_cache/
+.mypy_cache/
+.dmypy.json
+dmypy.json
+.pyre/
+.pytype/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# Ruff
+.ruff_cache/
+
+# uv
+.uv_cache/