feat(toc): add sticky positioning and entry animation for improved UX

src/styles/header-dividing.scss

@@ -10,6 +10,10 @@
   --dash-spacing: 10px;
   --dash-width: 2px;
 
+  // 进入动画初始状态（仅 sticky 激活时播放）
+  opacity: 1;
+  transition: opacity 0.3s ease-in-out;
+
   // 虚线背景层 - 带遮罩
   &::before {
     content: '';
@@ -81,6 +85,10 @@
     opacity: 0.8;
     box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
 
+    /* 进入动画：透明度由0到1，宽度由中间到100% */
+    animation: sticky-in 0.5s ease-in-out forwards;
+    opacity: 1;
+
     &::before {
       animation: line-flow 1.5s linear infinite;
       mask-image: none;
@@ -126,4 +134,13 @@
     left: 80%;
     opacity: 0;
   }
-}
+}
+
+@keyframes sticky-in {
+  0% {
+    opacity: 0;
+  }
+  100% {
+    opacity: 1;
+  }
+}

src/styles/post-toc.scss

@@ -1,14 +1,21 @@
 @import "variables";
 
+.post-toc-sticky {
+  position: sticky;
+  top: 0;
+  z-index: 100;
+  width: 0;
+  height: 0;
+  overflow: visible;
+  transform: translate(-260px, 100px);
+}
+
 .post-toc {
-  position: absolute;
-  left: -280px;
-  top: 85px;
+  position: relative;
   width: 200px;
   max-height: calc(100vh - 200px);
   overflow-y: auto;
   overflow-x: hidden;
-  z-index: 100;
   font-size: 0.8rem;
   line-height: 1.6;
   color: var(--foreground);
@@ -126,6 +133,18 @@
     transition: color 0.15s ease, opacity 0.15s ease;
   }
 
+  // 左侧激活指示线
+  &::before {
+    content: '' !important;
+    position: absolute;
+    left: -10px !important;
+    top: 4px;
+    bottom: 4px;
+    width: 2px;
+    background-color: transparent;
+    border-radius: 1px;
+  }
+
   // 活跃状态
   &--active {
     background-color: color-mix(in srgb, var(--brightBlue) 15%, transparent);
@@ -139,16 +158,8 @@
       color: var(--brightBlue);
     }
 
-    // 左侧激活指示线
     &::before {
-      content: '' !important;
-      position: absolute;
-      left: -10px !important;
-      top: 4px;
-      bottom: 4px;
-      width: 2px;
       background-color: var(--brightBlue);
-      border-radius: 1px;
     }
   }
 }
@@ -178,7 +189,7 @@
 
   &__icon {
     margin-right: 6px;
-    color: var(--yellow);
+    color: var(--red);
   }
 
   &__title {