feat(core): add application layer components

Add application layer:
- UseCase base class for use cases
- ResponseDto for standardized responses
- Mapper for domain-DTO conversion

packages/core/src/application/dtos/ResponseDto.ts

@@ -0,0 +1,31 @@
+/**
+ * Standard response wrapper for use cases
+ */
+export interface IResponseDto<T> {
+    success: boolean;
+    data?: T;
+    error?: string;
+    timestamp: Date;
+}
+
+export class ResponseDto<T> implements IResponseDto<T> {
+    public readonly success: boolean;
+    public readonly data?: T;
+    public readonly error?: string;
+    public readonly timestamp: Date;
+
+    private constructor(success: boolean, data?: T, error?: string) {
+        this.success = success;
+        this.data = data;
+        this.error = error;
+        this.timestamp = new Date();
+    }
+
+    public static ok<T>(data: T): ResponseDto<T> {
+        return new ResponseDto<T>(true, data);
+    }
+
+    public static fail<T>(error: string): ResponseDto<T> {
+        return new ResponseDto<T>(false, undefined, error);
+    }
+}