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.

frontend/app/api/document-import-proxy/route.ts

@@ -0,0 +1,20 @@
+import { NextRequest, NextResponse } from 'next/server';
+
+const API_BASE = process.env.NEXT_PUBLIC_API_URL_INTERNAL || 'http://localhost:3001';
+
+/**
+ * Proxy för POST /api/document-import
+ * Vidarebefordrar multipart/form-data till backend direkt (ingen JSON-omvandling)
+ */
+export async function POST(request: NextRequest) {
+  const formData = await request.formData();
+
+  const res = await fetch(`${API_BASE}/api/document-import`, {
+    method: 'POST',
+    body: formData,
+    // Sätt INTE Content-Type manuellt — browser sätter boundary automatiskt
+  });
+
+  const data = await res.json();
+  return NextResponse.json(data, { status: res.status });
+}