feat: Implement PDF document import functionality with Markdown conversion

- Added DocumentImportModule, DocumentImportController, and DocumentImportService for handling PDF uploads.
- Integrated pdf-parse for extracting text from PDF files.
- Created PdfParser for parsing PDF documents and converting them to Markdown format.
- Updated frontend to support file uploads via drag-and-drop and file input for PDF documents.
- Modified API routes to handle document import requests.
- Enhanced error handling for unsupported file types and file size limits.
- Updated README to reflect new features and usage instructions.

backend/package.json

@@ -13,14 +13,19 @@
     "@nestjs/platform-express": "^10.3.0",
     "class-transformer": "^0.5.1",
     "class-validator": "^0.15.1",
+    "multer": "^1.4.5-lts.1",
+    "pdf-parse": "^1.1.1",
     "reflect-metadata": "^0.2.2",
-    "rxjs": "^7.8.1"
+    "rxjs": "^7.8.1",
+    "tesseract.js": "^5.1.1"
   },
   "devDependencies": {
     "@nestjs/cli": "^10.3.0",
     "@nestjs/schematics": "^10.1.1",
     "@types/express": "^4.17.21",
+    "@types/multer": "^1.4.12",
     "@types/node": "^22.15.29",
+    "@types/pdf-parse": "^1.1.4",
     "typescript": "^5.4.5"
   }
 }