feat(posts): add preview URL fields for post images

Add PreviewURL and PreviewURLLarge fields to PostImage model and responses. Image data now supports format "url|preview_url|preview_url_large" for storing multiple image variants. Also change comment cursor pagination to sort by created_at ASC (oldest first) to display earliest comments as first floor, and make AdminReviewVerificationRequest.Approve field optional.

internal/service/admin_post_service.go

@@ -256,11 +256,13 @@ func convertPostToAdminListResponse(post *model.Post) dto.AdminPostListResponse
 	images := make([]dto.PostImageResponse, len(post.Images))
 	for i, img := range post.Images {
 		images[i] = dto.PostImageResponse{
-			ID:           img.ID,
-			URL:          img.URL,
-			ThumbnailURL: img.ThumbnailURL,
-			Width:        img.Width,
-			Height:       img.Height,
+			ID:              img.ID,
+			URL:             img.URL,
+			ThumbnailURL:    img.ThumbnailURL,
+			PreviewURL:      img.PreviewURL,
+			PreviewURLLarge: img.PreviewURLLarge,
+			Width:           img.Width,
+			Height:          img.Height,
 		}
 	}
 
@@ -298,11 +300,13 @@ func convertPostToAdminDetailResponse(post *model.Post) *dto.AdminPostDetailResp
 	images := make([]dto.PostImageResponse, len(post.Images))
 	for i, img := range post.Images {
 		images[i] = dto.PostImageResponse{
-			ID:           img.ID,
-			URL:          img.URL,
-			ThumbnailURL: img.ThumbnailURL,
-			Width:        img.Width,
-			Height:       img.Height,
+			ID:              img.ID,
+			URL:             img.URL,
+			ThumbnailURL:    img.ThumbnailURL,
+			PreviewURL:      img.PreviewURL,
+			PreviewURLLarge: img.PreviewURLLarge,
+			Width:           img.Width,
+			Height:          img.Height,
 		}
 	}