feat: 优化 Mermaid 拖拽功能

- 7.1 改进拖拽响应：使用 requestAnimationFrame 优化性能，避免频繁的 DOM 操作
- 7.2 优化拖拽视觉反馈：增强光标样式，添加跨浏览器的文本选择禁用
- 7.3 智能启用拖拽：检测图表是否需要拖拽，未缩放且完全可见时自动禁用

需求：13.1, 13.2, 13.3, 13.4, 13.5

argontheme.js

@@ -5775,12 +5775,47 @@ void 0;
 			let startY = 0;
 			let scrollLeft = 0;
 			let scrollTop = 0;
+			let rafId = null;
+			let pendingX = 0;
+			let pendingY = 0;
+
+			// 需求 13.5: 智能启用拖拽 - 检查图表是否需要拖拽
+			const checkDragEnabled = () => {
+				const svgElement = inner.querySelector('svg');
+				if (!svgElement) return false;
+				
+				// 如果图表未缩放且完全可见，禁用拖拽
+				const containerRect = container.getBoundingClientRect();
+				const svgRect = svgElement.getBoundingClientRect();
+				const isFullyVisible = svgRect.width <= containerRect.width && 
+				                       svgRect.height <= containerRect.height;
+				const isNotZoomed = Math.abs(scale - 1) < 0.01;
+				
+				return !(isFullyVisible && isNotZoomed);
+			};
+
+			// 需求 13.3: 使用 requestAnimationFrame 优化拖拽性能
+			const updateDragPosition = () => {
+				if (!isDragging) {
+					rafId = null;
+					return;
+				}
+				
+				inner.scrollLeft = scrollLeft - pendingX;
+				inner.scrollTop = scrollTop - pendingY;
+				
+				rafId = requestAnimationFrame(updateDragPosition);
+			};
 
 			inner.addEventListener('mousedown', (e) => {
 				// 只响应左键
 				if (e.button !== 0) return;
 				
+				// 需求 13.5: 检查是否需要启用拖拽
+				if (!checkDragEnabled()) return;
+				
 				isDragging = true;
+				// 需求 13.1: 改变鼠标光标为抓手样式
 				inner.classList.add('dragging');
 				
 				startX = e.pageX - inner.offsetLeft;
@@ -5788,7 +5823,13 @@ void 0;
 				scrollLeft = inner.scrollLeft;
 				scrollTop = inner.scrollTop;
 				
+				// 需求 13.2: 禁用文本选择
 				e.preventDefault();
+				
+				// 启动 RAF 循环
+				if (!rafId) {
+					rafId = requestAnimationFrame(updateDragPosition);
+				}
 			});
 
 			document.addEventListener('mousemove', (e) => {
@@ -5798,17 +5839,21 @@ void 0;
 				
 				const x = e.pageX - inner.offsetLeft;
 				const y = e.pageY - inner.offsetTop;
-				const walkX = (x - startX) * 2;
-				const walkY = (y - startY) * 2;
-				
-				inner.scrollLeft = scrollLeft - walkX;
-				inner.scrollTop = scrollTop - walkY;
+				// 更新待处理的位置，由 RAF 循环处理
+				pendingX = (x - startX) * 2;
+				pendingY = (y - startY) * 2;
 			});
 
 			document.addEventListener('mouseup', () => {
 				if (isDragging) {
 					isDragging = false;
+					// 需求 13.4: 恢复正常光标
 					inner.classList.remove('dragging');
+					// 取消 RAF 循环
+					if (rafId) {
+						cancelAnimationFrame(rafId);
+						rafId = null;
+					}
 				}
 			});
 
@@ -5817,6 +5862,13 @@ void 0;
 				e.preventDefault();
 			});
 			
+			// 需求 13.2: 禁用文本选择
+			inner.addEventListener('selectstart', (e) => {
+				if (isDragging) {
+					e.preventDefault();
+				}
+			});
+
 			// 需求 12.5: 双击智能缩放
 			// 双击图表时，如果当前是默认大小则放大到 2 倍，否则重置到 1 倍
 			inner.addEventListener('dblclick', (e) => {

style.css

@@ -1053,7 +1053,6 @@ html.darkmode .mermaid-zoom-controls {
 html.darkmode .mermaid-zoom-level {
 	color: #aaa;
 }
-}
 
 /* 按钮 tooltip */
 .mermaid-zoom-btn[title] {
@@ -1114,16 +1113,28 @@ html.darkmode .mermaid-hint {
 	backdrop-filter: blur(10px);
 }
 
-/* 拖拽时的光标 */
+/* 拖拽时的光标和视觉反馈 */
+/* 需求 13.1, 13.2, 13.4: 优化拖拽视觉反馈 */
 .mermaid-container-inner.dragging {
 	cursor: grabbing !important;
 	user-select: none;
+	-webkit-user-select: none;
+	-moz-user-select: none;
+	-ms-user-select: none;
 }
 
 .mermaid-container-inner:not(.dragging) {
 	cursor: grab;
 }
 
+/* 拖拽时禁用 SVG 内的文本选择 */
+.mermaid-container-inner.dragging svg {
+	user-select: none;
+	-webkit-user-select: none;
+	-moz-user-select: none;
+	-ms-user-select: none;
+}
+
 /* Mermaid 淡入动画 */
 @keyframes mermaidFadeIn {
 	from {