Add demo logic for landing

src/main/java/ru/soune/nocopy/dto/demo/DemoUploadRequest.java

@@ -0,0 +1,17 @@
+package ru.soune.nocopy.dto.demo;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class DemoUploadRequest {
+    private String fileName;
+    private String fileType; // "image", "document", "audio"
+    private Long fileSize;
+    private String mimeType;
+}