feat: integrate MinerU document to Markdown converter

- Add MinerU converter engine (src/converters/mineru.ts)
- Support md-t (table as Markdown) and md-i (table as image) output formats
- Input formats: pdf, ppt, pptx, xls, xlsx, doc, docx
- Output as ZIP archive containing Markdown and images
- Update Dockerfile to install magic-pdf via pipx
- Add zip utility for archive creation
- Update normalizeFiletype to map md-t/md-i to zip extension
- Add comprehensive tests for MinerU converter
- Update README with MinerU documentation

Dockerfile

@@ -139,8 +139,10 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   pipx \
   # === 系統工具 ===
   locales \
+  zip \
   # === 清理 ===
   && pipx install "markitdown[all]" \
+  && pipx install magic-pdf \
   # 清理 apt cache
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/* \