对接文档配色优化：分组标题品牌蓝+分隔线，接口项/子项灰阶拉开，小节标题蓝竖线区分

frontend/src/index.css

@@ -327,11 +327,16 @@ a {
   gap: 2px;
 }
 
+.api-docs__nav-group + .api-docs__nav-group {
+  border-top: 1px solid #e7edf5;
+  padding-top: 12px;
+}
+
 .api-docs__nav-heading {
   padding: 0 10px 8px;
   font-size: 14px;
   font-weight: 700;
-  color: #4e5969;
+  color: #1677ff;
   letter-spacing: 0.5px;
 }
 
@@ -345,7 +350,7 @@ a {
   min-height: 36px;
   padding: 8px 12px;
   font-size: 14px;
-  color: #4e5969;
+  color: #3d4553;
   cursor: pointer;
   border-radius: 5px;
   transition: all 0.15s;
@@ -379,7 +384,7 @@ a {
   min-height: 32px;
   padding: 6px 10px;
   font-size: 13.5px;
-  color: #5a6472;
+  color: #7a8599;
 }
 
 .api-docs__nav-sub-item--active {
@@ -476,15 +481,17 @@ a {
 .doc-section-title {
   font-size: 16px;
   font-weight: 700;
-  color: #1d2129;
+  color: #1f3a6e;
   margin: 22px 0 12px;
   scroll-margin-top: 24px;
+  padding-left: 10px;
+  border-left: 3px solid #1677ff;
 }
 
 .doc-subtitle {
   font-size: 14px;
   font-weight: 600;
-  color: #4e5969;
+  color: #3d4553;
   margin: 10px 0 10px;
 }