v0.0.3: refactor: Convert plugin from Node.js to Python

- Dify plugins only support Python runtime
- Added main.py entry point
- Added provider/gptproto_image.py for credential validation
- Added tools/text_to_image.py for image generation
- Updated manifest.yaml for Python runner
- Added requirements.txt with dependencies
- Fixed icon paths for packaging

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