feat(llm): Add Ollama provider and PyMuPDF image extraction

This commit introduces support for Ollama as an alternative Large Language Model (LLM) provider and enhances PDF image extraction capabilities.

- **Ollama Integration:**
    - Implemented `set_ollama_config` to configure Ollama's base URL from `config.ini`.
    - Modified `llm.py` to dynamically select and configure the LLM (Gemini or Ollama) based on the `PROVIDER` setting.
    - Updated `get_model_name` to return provider-specific default model names.
    - `pdf_convertor.py` now conditionally initializes `ChatGoogleGenerativeAI` or `ChatOllama` based on the configured provider.
- **PyMuPDF Image Extraction:**
    - Added a new `extract_images_from_pdf` function using PyMuPDF (`fitz`) for direct image extraction from PDF files.
    - Introduced `get_extract_images_from_pdf_flag` to control this feature via `config.ini`.
    - `convert_pdf_to_markdown` and `refine_content` functions were updated to utilize this new image extraction method when enabled.
- **Refinement Flow:**
    - Adjusted the order of `save_md_images` in `main.py` and added an option to save the refined markdown with a specific filename (`index_refined.md`).
- **Dependencies:**
    - Updated `pyproject.lock` to include new dependencies for Ollama integration (`langchain-ollama`) and PyMuPDF (`PyMuPDF`), along with platform-specific markers for NVIDIA dependencies.

pyproject.toml

@@ -7,6 +7,8 @@ requires-python = ">=3.13"
 dependencies = [
     "docling>=2.57.0",
     "langchain>=1.0.2",
+    "langchain-community>=0.4.1",
     "langchain-google-genai>=3.0.0",
     "langchain-ollama>=1.0.0",
+    "pymupdf>=1.26.6",
 ]