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/dto/dto.go

@@ -1404,7 +1404,7 @@ type AdminVerificationDetailResponse struct {
 
 // AdminReviewVerificationRequest 管理端审核认证请求
 type AdminReviewVerificationRequest struct {
-	Approve      bool   `json:"approve" binding:"required"`
+	Approve      bool   `json:"approve"`
 	RejectReason string `json:"reject_reason" binding:"omitempty,max=500"`
 }
 

internal/dto/post_converter.go

@@ -14,11 +14,13 @@ func ConvertPostImageToResponse(img *model.PostImage) PostImageResponse {
 		return PostImageResponse{}
 	}
 	return 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,
 	}
 }