refactor: remove all document conversion support, keep only media conversions

This commit completely removes document conversion functionality to focus
exclusively on media file conversions (video, audio, images).

Changes:
- Remove all document converter services (pandocService.ts, pdfService.ts, docxService.ts)
- Uninstall document-related packages: marked, turndown, dompurify, jspdf, pdfjs-dist, docx, mammoth, @types/turndown
- Remove document formats (PDF, DOCX, Markdown, HTML, TXT) from formatMappings.ts
- Remove pandoc converter from FileConverter.tsx
- Remove pandoc loader and references from wasmLoader.ts
- Update TypeScript types to remove 'pandoc' from ConverterEngine and 'document' from FileCategory
- Remove pandoc from WASMModuleState interface
- Update README.md to remove all document conversion documentation
- Update UI descriptions to reflect media-only conversions

Supported conversions now:
- Video: MP4, WebM, AVI, MOV, MKV, GIF
- Audio: MP3, WAV, OGG, AAC, FLAC
- Images: PNG, JPG, WebP, GIF, BMP, TIFF, SVG

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -13,26 +13,18 @@
     "@ffmpeg/util": "^0.12.1",
     "@imagemagick/magick-wasm": "^0.0.30",
     "clsx": "^2.1.1",
-    "docx": "^9.0.4",
-    "dompurify": "^3.2.2",
     "fuse.js": "^7.1.0",
-    "jspdf": "^2.5.2",
     "lucide-react": "^0.553.0",
-    "mammoth": "^1.8.0",
-    "marked": "^15.0.4",
     "next": "^16.0.0",
-    "pdfjs-dist": "^4.10.38",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
-    "tailwind-merge": "^3.3.1",
-    "turndown": "^7.2.0"
+    "tailwind-merge": "^3.3.1"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4.1.17",
     "@types/node": "^22",
     "@types/react": "^19",
     "@types/react-dom": "^19",
-    "@types/turndown": "^5.0.5",
     "eslint": "^9",
     "eslint-config-next": "^16.0.0",
     "tailwindcss": "^4.0.0",