Scope 1s tick interval to Chart component to eliminate page-level re-renders

The setInterval that drives the "Live · Xs ago" display was at the page level,
forcing all 10+ dashboard components to re-render every second. Now it lives
inside Chart — the only consumer — so the rest of the dashboard is unaffected.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/sites/[id]/page.tsx

@@ -100,7 +100,6 @@ export default function SiteDashboardPage() {
   const [isDatePickerOpen, setIsDatePickerOpen] = useState(false)
   const [isExportModalOpen, setIsExportModalOpen] = useState(false)
   const lastUpdatedAtRef = useRef<number | null>(null)
-  const [, setTick] = useState(0)
 
   // Dimension filters state
   const searchParams = useSearchParams()
@@ -374,12 +373,6 @@ export default function SiteDashboardPage() {
     if (overview) lastUpdatedAtRef.current = Date.now()
   }, [overview])
 
-  // Tick every 1s so "Live · Xs ago" counts in real time
-  useEffect(() => {
-    const timer = setInterval(() => setTick((t) => t + 1), 1000)
-    return () => clearInterval(timer)
-  }, [])
-
   // Save settings to localStorage
   const saveSettings = (type: string, newDateRange?: { start: string; end: string }) => {
     try {

components/dashboard/Chart.tsx

@@ -161,6 +161,14 @@ export default function Chart({
   const { resolvedTheme } = useTheme()
   const [showComparison, setShowComparison] = useState(false)
 
+  // Tick every 1s so "Live · Xs ago" counts in real time (scoped to Chart only)
+  const [, setTick] = useState(0)
+  useEffect(() => {
+    if (lastUpdatedAt == null) return
+    const timer = setInterval(() => setTick((t) => t + 1), 1000)
+    return () => clearInterval(timer)
+  }, [lastUpdatedAt])
+
   // ─── Annotation state ─────────────────────────────────────────────
   const [annotationForm, setAnnotationForm] = useState<{
     visible: boolean; editingId?: string; date: string; time: string; text: string; category: string