fix: align group analytics header layout

src/pages/GroupAnalyticsPage.scss

@@ -1,6 +1,14 @@
+.group-analytics-shell {
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+  min-height: 100%;
+}
+
 .group-analytics-page {
   display: flex;
-  height: 100%;
+  flex: 1;
+  min-height: 0;
   gap: 16px;
 
   &.standalone {
@@ -463,10 +471,6 @@
   background: var(--bg-secondary);
   border-radius: 16px;
   overflow: hidden;
-
-  .chat-analysis-header {
-    margin: 16px 16px 0;
-  }
 }
 
 .resize-handle {

src/pages/GroupAnalyticsPage.tsx

@@ -1186,12 +1186,14 @@ function GroupAnalyticsPage() {
   }
 
   return (
-    <div className={`group-analytics-page ${isResizing ? 'resizing' : ''}`} ref={containerRef}>
-      {renderGroupList()}
-      <div className="resize-handle" onMouseDown={() => setIsResizing(true)} />
-      <div className="detail-area">
-        <ChatAnalysisHeader currentMode="group" />
-        {renderDetailPanel()}
+    <div className="group-analytics-shell">
+      <ChatAnalysisHeader currentMode="group" />
+      <div className={`group-analytics-page ${isResizing ? 'resizing' : ''}`} ref={containerRef}>
+        {renderGroupList()}
+        <div className="resize-handle" onMouseDown={() => setIsResizing(true)} />
+        <div className="detail-area">
+          {renderDetailPanel()}
+        </div>
       </div>
       {renderMemberModal()}
     </div>