新增 EQ撤销功能，用户调节的参数不满意可以点击回退到上一次，撤销栈最多存放 30 步

client/src/pages/eq/components/FreqChart.tsx

@@ -40,6 +40,8 @@ export function FreqChart({
   onApplyB,
   onSaveB,
   onBandDrag,
+  onBandDragStart,
+  onBandDragEnd,
   onBandSelect,
   eqUi,
 }: {
@@ -53,6 +55,8 @@ export function FreqChart({
   onApplyB: () => void;
   onSaveB: () => void;
   onBandDrag: (idx: number, patch: Partial<{ freq: number; gain: number }>) => void;
+  onBandDragStart?: () => void;
+  onBandDragEnd?: () => void;
   onBandSelect: (idx: number) => void;
   eqUi: PeqEqUi;
 }) {
@@ -118,6 +122,7 @@ export function FreqChart({
     e.stopPropagation();
     draggingBandRef.current = idx;
     setIsBandDragging(true);
+    onBandDragStart?.();
     onBandSelect(idx);
     updateBandFromPointer(idx, e.clientX, e.clientY);
   };
@@ -130,8 +135,10 @@ export function FreqChart({
   };
 
   const stopDragging = () => {
+    if (draggingBandRef.current === null) return;
     draggingBandRef.current = null;
     setIsBandDragging(false);
+    onBandDragEnd?.();
   };
 
   const curveData = useMemo(

client/src/pages/eq/components/PeqUndoButton.tsx

@@ -0,0 +1,46 @@
+import { Undo2 } from "lucide-react";
+import { cn } from "@/lib/utils";
+
+type PeqUndoButtonProps = {
+  disabled?: boolean;
+  label: string;
+  onClick: () => void;
+  className?: string;
+};
+
+/**
+ * EQ page undo control — disabled when the undo stack is empty.
+ */
+export function PeqUndoButton({
+  disabled = false,
+  label,
+  onClick,
+  className,
+}: PeqUndoButtonProps) {
+  return (
+    <button
+      type="button"
+      disabled={disabled}
+      aria-label={label}
+      title={label}
+      onClick={onClick}
+      className={cn(
+        "w-9 h-9 rounded-full flex items-center justify-center transition-colors active:scale-95",
+        disabled
+          ? "text-white/25 cursor-not-allowed"
+          : "text-white/70 active:text-white",
+        className,
+      )}
+      style={{
+        background: disabled
+          ? "rgba(44,44,46,0.45)"
+          : "rgba(44,44,46,0.8)",
+        border: disabled
+          ? "1px solid rgba(255,255,255,0.06)"
+          : "1px solid rgba(255,255,255,0.1)",
+      }}
+    >
+      <Undo2 size={18} />
+    </button>
+  );
+}