feat: enhance app.py with session state management and extraction strategy selection

feat: enhance architecture and developer documentation for clarity and detail

feat: update unique indices combinator to return array of objects

Revise documentation in app.py for Deep‑Research PDF Field Extractor, enhancing clarity on system architecture, core components, processing pipeline, and key features. Update usage instructions and support resources for better user guidance.

Update Azure OpenAI API version in settings and enhance logging in LLMClient for request URL

Add logging for settings initialization and update LLMClient to use settings for API version

Update Dockerfile to use new app entry point and enhance requirements.txt with additional dependencies. Remove obsolete streamlit_app.py file.