对接文档目录字号优化：分组标题 12→14px 加粗，接口项/子项同步放大，目录加宽

frontend/src/index.css

@@ -281,8 +281,8 @@ a {
 
 /* 左侧目录 */
 .api-docs__toc {
-  flex: 0 0 220px;
-  width: 220px;
+  flex: 0 0 240px;
+  width: 240px;
   height: 100%;
   overflow-y: auto;
   border-right: 1px solid #e7edf5;
@@ -318,7 +318,7 @@ a {
 .api-docs__nav {
   display: flex;
   flex-direction: column;
-  gap: 14px;
+  gap: 16px;
 }
 
 .api-docs__nav-group {
@@ -328,9 +328,11 @@ a {
 }
 
 .api-docs__nav-heading {
-  padding: 0 10px 6px;
-  font-size: 12px;
-  color: #9aa4b2;
+  padding: 0 10px 8px;
+  font-size: 14px;
+  font-weight: 700;
+  color: #4e5969;
+  letter-spacing: 0.5px;
 }
 
 .api-docs__nav-row {
@@ -340,9 +342,9 @@ a {
 .api-docs__nav-item,
 .api-docs__nav-sub-item {
   display: block;
-  min-height: 32px;
-  padding: 7px 12px;
-  font-size: 13px;
+  min-height: 36px;
+  padding: 8px 12px;
+  font-size: 14px;
   color: #4e5969;
   cursor: pointer;
   border-radius: 5px;
@@ -374,10 +376,10 @@ a {
 }
 
 .api-docs__nav-sub-item {
-  min-height: 28px;
-  padding: 5px 10px;
-  font-size: 12.5px;
-  color: #86909c;
+  min-height: 32px;
+  padding: 6px 10px;
+  font-size: 13.5px;
+  color: #5a6472;
 }
 
 .api-docs__nav-sub-item--active {