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

src/helpers/normalizeFiletype.ts

@@ -31,6 +31,10 @@ export const normalizeOutputFiletype = (filetype: string): string => {
     case "markdown_mmd":
     case "markdown":
       return "md";
+    // MinerU output formats - output as ZIP
+    case "md-t":
+    case "md-i":
+      return "zip";
     default:
       return lowercaseFiletype;
   }