feat: 四圆角独立处理 + transform rotate

- 圆角：取四角最大值（PPT只支持统一圆角）
- 旋转：CSS transform:rotate → pptxgenjs rotate
- 两个文件同步

web-to-ppt/convert-browser.js

@@ -476,8 +476,7 @@ async function convertToPptx(input, onProgress) {
         // 形状类型
         var useShape = 'rect';
         if (shapeOpts.rectRadius) {
-          var brPct = parseFloat(n.styles.borderTopLeftRadius);
-          var isCircle = (brPct >= 50 || (brPct.toString().includes('%') && parseFloat(brPct) >= 50)) && Math.abs(opts.w - opts.h) < 0.05;
+          var isCircle = shapeOpts.rectRadius >= 0.5 && Math.abs(opts.w - opts.h) < 0.05;
           useShape = isCircle ? 'ellipse' : 'roundRect';
         }
         objects.push({ type: 'shape', shapeName: useShape, options: shapeOpts });