refactor: 统一使用 OpenAI 兼容 API，支持自定义 base_url/key/model

- 移除 Gemini 和 Ollama 独立适配，统一使用 ChatOpenAI + base_url
- config.ini 简化为 BASE_URL / API_KEY / MODEL / TEMPERATURE / MAX_RETRIES
- 新增 config.example.ini 示例配置
- 移除 langchain-google-genai / langchain-ollama / pymupdf 依赖
- main.py 新增断点续跑：跳过已有 index.md / index_refined.md
- LLM 请求支持 max_retries 自动重试（默认 3 次）
- 优化 README

main.py

@@ -1,6 +1,7 @@
 import os
 from pdf_convertor import (
     convert_pdf_to_markdown,
+    load_md_file,
     save_md_images,
     refine_content,
 )
@@ -24,12 +25,29 @@ def main():
 
         current_output_dir.mkdir(parents=True, exist_ok=True)
 
+        index_md = current_output_dir / "index.md"
+        refined_md = current_output_dir / "index_refined.md"
+
+        # 整个跳过：已存在精炼结果，跳过该文件
+        if refined_md.exists():
+            print(f"Skipping {pdf_path.name}: already processed (index_refined.md exists)")
+            continue
+
         print(f"Processing {pdf_path} -> {current_output_dir}")
 
         with open(pdf_path, "rb") as pdf_file:
             pdf_content = pdf_file.read()
-            md, images = convert_pdf_to_markdown(pdf_content)
-            save_md_images(current_output_dir, md, images)
+
+            # 部分跳过：已存在转换结果，跳过 PDF 转 MD
+            if index_md.exists():
+                print(f"  Skipping PDF→MD conversion: index.md already exists")
+                md, images = load_md_file(index_md)
+            else:
+                md, images = convert_pdf_to_markdown(pdf_content)
+                save_md_images(current_output_dir, md, images)
+
+            # 部分跳过：已存在精炼结果，跳过 LLM 精炼
+            # (前面已检查整个跳过，这里不需要再检查)
 
             try:
                 md = refine_content(md, images, pdf_content)