Fix Sidebar render purity for history bucket grouping

src/components/layout/Sidebar.tsx

@@ -3,7 +3,7 @@
  * Navigation sidebar with menu items.
  * No longer fixed - sits inside the flex layout below the title bar.
  */
-import { useState } from 'react';
+import { useEffect, useState } from 'react';
 import { NavLink, useLocation, useNavigate } from 'react-router-dom';
 import {
   Home,
@@ -92,6 +92,8 @@ function getSessionBucket(activityMs: number, nowMs: number): SessionBucketKey {
   return 'older';
 }
 
+const INITIAL_NOW_MS = Date.now();
+
 export function Sidebar() {
   const sidebarCollapsed = useSettingsStore((state) => state.sidebarCollapsed);
   const setSidebarCollapsed = useSettingsStore((state) => state.setSidebarCollapsed);
@@ -130,7 +132,14 @@ export function Sidebar() {
 
   const { t } = useTranslation(['common', 'chat']);
   const [sessionToDelete, setSessionToDelete] = useState<{ key: string; label: string } | null>(null);
-  const nowMs = Date.now();
+  const [nowMs, setNowMs] = useState(INITIAL_NOW_MS);
+
+  useEffect(() => {
+    const timer = window.setInterval(() => {
+      setNowMs(Date.now());
+    }, 60 * 1000);
+    return () => window.clearInterval(timer);
+  }, []);
   const sessionBuckets: Array<{ key: SessionBucketKey; label: string; sessions: typeof sessions }> = [
     { key: 'today', label: t('chat:historyBuckets.today'), sessions: [] },
     { key: 'yesterday', label: t('chat:historyBuckets.yesterday'), sessions: [] },