fix(planting-service): 签名图片保持原始尺寸放置

- 不再缩放签名图片适应按钮大小
- 直接在按钮位置绘制原始尺寸的签名
- 避免签名被压扁变形

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/services/planting-service/src/infrastructure/pdf/pdf-generator.service.ts

@@ -382,48 +382,31 @@ export class PdfGeneratorService {
           const form = pdfDoc.getForm();
           const signatureButton = form.getButton(FORM_FIELDS.SIGNATURE);
 
-          // 获取按钮的 widget 和尺寸
+          // 获取按钮的 widget 和位置
           const widgets = signatureButton.acroField.getWidgets();
           if (widgets.length > 0) {
             const widget = widgets[0];
             const rect = widget.getRectangle();
-            const { width: fieldWidth, height: fieldHeight } = rect;
 
-            // 计算图片缩放尺寸（保持宽高比，适应字段大小）
+            // 获取签名图片原始尺寸
             const imgDims = signatureImage.scale(1);
-            let scale = Math.min(fieldWidth / imgDims.width, fieldHeight / imgDims.height);
-            const scaledWidth = imgDims.width * scale;
-            const scaledHeight = imgDims.height * scale;
+            const imgWidth = imgDims.width;
+            const imgHeight = imgDims.height;
 
-            // 计算居中位置
-            const x = (fieldWidth - scaledWidth) / 2;
-            const y = (fieldHeight - scaledHeight) / 2;
+            // 直接在按钮位置绘制原始尺寸的签名图片
+            // 获取按钮所在的页面
+            const pages = pdfDoc.getPages();
+            const page = pages[5]; // 第6页（签名区域）
 
-            // 创建外观流内容
-            const appearanceStream = `q ${scaledWidth} 0 0 ${scaledHeight} ${x} ${y} cm /Img Do Q`;
-
-            // 创建 XObject Form 作为外观
-            const context = pdfDoc.context;
-            const imageXObjectName = 'Img';
-
-            const Resources = context.obj({
-              XObject: { [imageXObjectName]: signatureImage.ref },
+            // 在按钮的左下角位置绘制签名图片（保持原始尺寸）
+            page.drawImage(signatureImage, {
+              x: rect.x,
+              y: rect.y,
+              width: imgWidth,
+              height: imgHeight,
             });
 
-            const appearanceStreamRef = context.register(
-              context.stream(appearanceStream, {
-                Type: 'XObject',
-                Subtype: 'Form',
-                FormType: 1,
-                BBox: [0, 0, fieldWidth, fieldHeight],
-                Resources,
-              }),
-            );
-
-            // 设置外观到 widget
-            widget.setNormalAppearance(appearanceStreamRef);
-
-            this.logger.log('Signature embedded using custom appearance stream');
+            this.logger.log(`Signature embedded at (${rect.x}, ${rect.y}) with original size ${imgWidth}x${imgHeight}`);
           } else {
             throw new Error('No widgets found for signature button');
           }