fix: ENOENT download error for archive-only converters (PDFMathTranslate/MinerU)

- Add existsSync checks in download.tsx before file access
- Fix normalizeFiletype.ts: md-t/md-i return original format (not tar.gz)
- Add outputMode: 'archive' support in main.ts with auto .tar suffix
- PDFMathTranslate outputs translated-<lang>.pdf + bilingual-<lang>.pdf (no original)
- MinerU outputs complete folder in .tar with logging
- Hide preview icon for .tar files in results.tsx
- Update Bun version: 1.2.2 -> 1.3.6
- Add Step 19: auto-deploy to remote server after Docker push

All 159 tests pass.

src/helpers/normalizeFiletype.ts

@@ -31,10 +31,11 @@ export const normalizeOutputFiletype = (filetype: string): string => {
     case "markdown_mmd":
     case "markdown":
       return "md";
-    // MinerU output formats - output as tar.gz
+    // MinerU output formats - 保持原始格式名稱（.tar 由 main.ts 自動添加）
+    // 因為 MinerU 是 archive-only 引擎，outputMode: "archive"
     case "md-t":
     case "md-i":
-      return "tar.gz";
+      return lowercaseFiletype;
     default:
       return lowercaseFiletype;
   }