feat(PdfViewer): 添加双指缩放手势支持

实现PDF查看器的双指缩放功能，包括触摸开始、移动和结束的完整手势处理

@@ -536,18 +536,117 @@ const addPreventSaveListeners = () => {
             return false;
         });
 
-        // 防止触摸回调（移动端长按）
-        pdfContainer.addEventListener('touchstart', (e) => {
-            if (e.touches.length > 1) {
-                e.preventDefault();
-            }
-        });
+        // 添加双指缩放手势支持
+        addPinchZoomListeners(pdfContainer);
+    }
+};
 
-        // 防止双指缩放等手势
-        pdfContainer.addEventListener('gesturestart', (e) => {
+// 双指缩放相关变量
+let initialDistance = 0;
+let initialZoom = 1;
+let isZooming = false;
+
+/**
+ * 添加双指缩放手势监听器
+ */
+const addPinchZoomListeners = (container) => {
+    let touches = [];
+
+    // 计算两点间距离
+    const getDistance = (touch1, touch2) => {
+        const dx = touch1.clientX - touch2.clientX;
+        const dy = touch1.clientY - touch2.clientY;
+        return Math.sqrt(dx * dx + dy * dy);
+    };
+
+    // 获取两点中心位置
+    const getCenter = (touch1, touch2) => {
+        return {
+            x: (touch1.clientX + touch2.clientX) / 2,
+            y: (touch1.clientY + touch2.clientY) / 2
+        };
+    };
+
+    // 触摸开始
+    container.addEventListener('touchstart', (e) => {
+        touches = Array.from(e.touches);
+        
+        if (touches.length === 2) {
+            // 双指触摸开始
             e.preventDefault();
-        });
-    }
+            isZooming = true;
+            initialDistance = getDistance(touches[0], touches[1]);
+            initialZoom = zoomLevel.value;
+        } else if (touches.length > 2) {
+            // 超过两指时阻止默认行为
+            e.preventDefault();
+        }
+    }, { passive: false });
+
+    // 触摸移动
+    container.addEventListener('touchmove', (e) => {
+        if (e.touches.length === 2 && isZooming) {
+            e.preventDefault();
+            
+            const currentTouches = Array.from(e.touches);
+            const currentDistance = getDistance(currentTouches[0], currentTouches[1]);
+            const scale = currentDistance / initialDistance;
+            
+            // 计算新的缩放级别
+            let newZoom = initialZoom * scale;
+            newZoom = Math.max(0.5, Math.min(3, newZoom)); // 限制缩放范围
+            
+            // 获取缩放中心点
+            const center = getCenter(currentTouches[0], currentTouches[1]);
+            const rect = container.getBoundingClientRect();
+            const centerX = center.x - rect.left;
+            const centerY = center.y - rect.top;
+            
+            // 应用缩放
+            applyPinchZoom(newZoom, centerX, centerY, container);
+        }
+    }, { passive: false });
+
+    // 触摸结束
+    container.addEventListener('touchend', (e) => {
+        if (isZooming && e.touches.length < 2) {
+            isZooming = false;
+            initialDistance = 0;
+            initialZoom = zoomLevel.value;
+        }
+    });
+
+    // 触摸取消
+    container.addEventListener('touchcancel', (e) => {
+        isZooming = false;
+        initialDistance = 0;
+        initialZoom = zoomLevel.value;
+    });
+};
+
+/**
+ * 应用双指缩放
+ */
+const applyPinchZoom = (newZoom, centerX, centerY, container) => {
+    const oldZoom = zoomLevel.value;
+    const oldScrollLeft = container.scrollLeft;
+    const oldScrollTop = container.scrollTop;
+    
+    // 更新缩放级别
+    zoomLevel.value = newZoom;
+    
+    // 等待DOM更新后调整滚动位置
+    nextTick(() => {
+        const zoomRatio = newZoom / oldZoom;
+        
+        // 计算新的滚动位置，以缩放中心为锚点
+        const newScrollLeft = (oldScrollLeft + centerX) * zoomRatio - centerX;
+        const newScrollTop = (oldScrollTop + centerY) * zoomRatio - centerY;
+        
+        // 应用新的滚动位置
+        container.scrollLeft = Math.max(0, newScrollLeft);
+        container.scrollTop = Math.max(0, newScrollTop);
+    });
 };
 </script>