修复PSD模板画布自动适配显示

- 添加自动缩放逻辑，确保模板完整显示在预览窗口内
- 避免模板超出预览区域，提升用户体验

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

components/agents/AgentPsdTemplateEditorDialog.tsx

@@ -471,6 +471,20 @@ export function AgentPsdTemplateEditorDialog({
     setImagePlacements(initialState.imagePlacements);
     setTextAssignments(initialState.textAssignments);
     setSelectedLayerId(getPreferredSelectedLayerId(selectedTemplate));
+
+    // 自动适配缩放比例
+    if (selectedTemplate && previewViewportRef.current) {
+      const viewport = previewViewportRef.current;
+      const padding = 32; // 预留边距
+      const availableWidth = viewport.clientWidth - padding;
+      const availableHeight = viewport.clientHeight - padding;
+
+      const scaleX = availableWidth / selectedTemplate.width;
+      const scaleY = availableHeight / selectedTemplate.height;
+      const fitScale = Math.min(scaleX, scaleY, 1); // 不超过1倍
+
+      setStageScale(fitScale);
+    }
   }, [open, selectedTemplate, sourceImageUrl]);
 
   useEffect(() => {