对接文档移除顶部「开放 API/API 密钥」切换按钮，统一由左侧目录导航

frontend/src/index.css

@@ -290,31 +290,6 @@ a {
   padding: 16px 12px 20px;
 }
 
-.api-docs__toc-tabs {
-  display: grid;
-  grid-template-columns: 1fr 1fr;
-  gap: 6px;
-  margin-bottom: 16px;
-}
-
-.api-docs__toc-tab {
-  height: 34px;
-  border: 0;
-  border-radius: 6px;
-  background: transparent;
-  color: #4e5969;
-  font-size: 13px;
-  font-weight: 600;
-  cursor: pointer;
-  transition: all 0.16s ease;
-}
-
-.api-docs__toc-tab:hover,
-.api-docs__toc-tab--active {
-  color: #1677ff;
-  background: #edf5ff;
-}
-
 .api-docs__nav {
   display: flex;
   flex-direction: column;

frontend/src/pages/OpenApiDocs.tsx

@@ -180,22 +180,6 @@ export default function OpenApiDocs() {
     <div className="api-docs">
       {/* 左侧目录 */}
       <aside className="api-docs__toc">
-        <div className="api-docs__toc-tabs">
-          <button
-            className={`api-docs__toc-tab${activePageId !== 'auth' ? ' api-docs__toc-tab--active' : ''}`}
-            type="button"
-            onClick={() => handleNav('overview')}
-          >
-            开放 API
-          </button>
-          <button
-            className={`api-docs__toc-tab${activePageId === 'auth' ? ' api-docs__toc-tab--active' : ''}`}
-            type="button"
-            onClick={() => handleNav('auth')}
-          >
-            API 密钥
-          </button>
-        </div>
         <nav className="api-docs__nav">
           {toc.map((group) => (
             <div className="api-docs__nav-group" key={group.title}>