feat: add multi-model provider support and uv integration

[dxpython]

Summary

This PR introduces major updates to PageIndex for broader model compatibility, faster developer setup, a new visualization interface, and algorithm improvements.

What’s included

• Added multi-model provider support:
  • DeepSeek
  • Qwen
  • Claude
  • Gemini
  • OpenRouter
  • Ollama
• Added UV package manager integration for faster and more reproducible environment setup.
• Added a React-based visualization UI for interacting with and inspecting PageIndex outputs.
• Added helper scripts and documentation updates for model switching, testing, and startup workflows.
• Fixed and improved core algorithm logic to increase stability and result quality.

Compatibility

• Fully backward compatible with the existing OpenAI workflow.
• Existing OpenAI-based .env configuration and runtime behavior remain supported.