Fix unused tick state causing TS build error in CpuChart

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

client/src/components/dashboard/CpuChart.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState } from "react"
+import { useEffect, useRef } from "react"
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card"
 import { cn } from "@/lib/utils"
 
@@ -32,17 +32,13 @@ function loadColor(load: number) {
 }
 
 export function CpuChart({ history, loadAvg }: CpuChartProps) {
-  const [tick, setTick] = useState(0)
   const prevLenRef = useRef(0)
   const currentCpu = history.length > 0 ? history[history.length - 1].cpuPercent : 0
   const color = cpuColor(currentCpu)
 
-  // Trigger CSS transition whenever a new point arrives
+  // Track history length changes (used to drive CSS transitions via key changes)
   useEffect(() => {
-    if (history.length !== prevLenRef.current) {
     prevLenRef.current = history.length
-      setTick(t => t + 1)
-    }
   }, [history.length])
 
   // Assign fixed x positions: latest point always at right edge, older ones to the left