- Implement upload_pdf_file method with file validation, size limits (50MB), and unique filename generation
  - Create serve_media_file API endpoint to serve PDF documents with URL decoding support
  - Update DocumentUploadController to accept user_id as required parameter
  - Add file organization structure: media/documents/{user_id}/{timestamp}_{uuid}_{filename}
  - Clean filename generation: remove spaces and special characters from uploaded files
  - Add URL route /api/core-ia/media/{user_id}/{file_name} for document access
  - Support multiple file formats (PDF, DOCX, DOC, TXT, images) in media serving
  - Include security checks for path traversal prevention
  - Add database migration for user_id field with default value 1 for existing records