style: solution彩色竖条加上下流动渐变动画

- 渐变色: 蓝→紫→粉→蓝 循环
- background-size: 300% 配合 background-position 动画
- 3s ease-in-out infinite 平滑流动

css/index.css

@@ -4472,7 +4472,7 @@ html {
   position: relative;
 }
 
-/* 左侧装饰竖线 */
+/* 左侧装饰竖线 — 渐变上下流动 */
 .solution-text::before {
   content: '';
   position: absolute;
@@ -4480,8 +4480,16 @@ html {
   top: 20%;
   height: 60%;
   width: 3px;
-  background: linear-gradient(180deg, transparent, #38BDF8, rgba(99, 102, 241, 0.6), transparent);
+  background: linear-gradient(180deg, transparent, #38BDF8, #6366F1, #EC4899, #38BDF8, transparent);
+  background-size: 100% 300%;
   border-radius: 3px;
+  animation: solutionBarFlow 3s ease-in-out infinite;
+}
+
+@keyframes solutionBarFlow {
+  0%   { background-position: 0% 0%; }
+  50%  { background-position: 0% 100%; }
+  100% { background-position: 0% 0%; }
 }
 
 .solution-text h3 {