main: update

feat: Automatically detect Poppler path and provide a download fallback with installation instructions when PDF rendering fails.

main : add features pdf viewer handler

main : fixing pdf viewer feature

main: Adding simple feature and fixing pdf viewer to no revert or citation action for every answer from ChatBot

feat: Implement an interactive document viewer with citation highlighting and structured PDF text extraction.

feat: Implement Speech-to-Text functionality for voice input in the Gradio interface, including a new utility, configurations, and UI components.

feat: Migrate the default LLM from ChatGLM3 to Qwen2-0.5B-Instruct, updating model loading, generation logic, and documentation.

refactor: Update `RecursiveCharacterTextSplitter` import to use `langchain_text_splitters` with a fallback to `langchain.text_splitter`.

feat: Implement initial RAG chatbot core functionalities including PDF processing, vector store, and RAG pipeline.