feat: Presigned URL API 및 OpenTelemetry trace 추가

- Presigned URL API 추가 (MinIO/S3 private 버킷 지원)
- OpenTelemetry trace 설정 추가 (DEBUG=False 시 활성화)
- requirements.txt에 opentelemetry 패키지 추가

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

blog/views.py

@@ -2,6 +2,9 @@
 
 import os
 import re
+import boto3
+from botocore.client import Config
+from django.conf import settings
 from rest_framework import generics, viewsets, permissions, status
 from rest_framework.exceptions import PermissionDenied
 from rest_framework.response import Response
@@ -371,4 +374,40 @@ class AttachmentDeleteView(APIView):
         attachment.delete()
 
         logger.info(f"Attachment '{original_name}' deleted from post {post_pk} by {username}.")
-        return Response(status=status.HTTP_204_NO_CONTENT)
+        return Response(status=status.HTTP_204_NO_CONTENT)
+
+
+class PresignedUrlView(APIView):
+    """Presigned URL 생성 (MinIO/S3)"""
+    permission_classes = [permissions.AllowAny]
+
+    def get_s3_client(self):
+        """S3 클라이언트 생성"""
+        return boto3.client(
+            's3',
+            endpoint_url=settings.AWS_S3_ENDPOINT_URL,
+            aws_access_key_id=settings.AWS_ACCESS_KEY_ID,
+            aws_secret_access_key=settings.AWS_SECRET_ACCESS_KEY,
+            config=Config(signature_version='s3v4'),
+            region_name=settings.AWS_S3_REGION_NAME,
+        )
+
+    def get(self, request, object_key):
+        """GET presigned URL 생성"""
+        try:
+            s3_client = self.get_s3_client()
+            presigned_url = s3_client.generate_presigned_url(
+                'get_object',
+                Params={
+                    'Bucket': settings.AWS_STORAGE_BUCKET_NAME,
+                    'Key': object_key,
+                },
+                ExpiresIn=3600,  # 1시간 유효
+            )
+            return Response({'url': presigned_url})
+        except Exception as e:
+            logger.error(f"Presigned URL 생성 실패: {e}")
+            return Response(
+                {'detail': 'Presigned URL 생성 실패'},
+                status=status.HTTP_500_INTERNAL_SERVER_ERROR
+            )