feat(eq): 使用平直曲线作为默认预设显示

- 新增 FLAT_BANDS 平直曲线预设，包含10个增益为0的PEAK滤波器
- 默认初始化bandsByMode状态使用FLAT_BANDS替代旧的DEFAULT_BANDS
- 在无远程peq数据或切换耳机时，默认设置为FLAT_BANDS
- 无滤波器时恢复平直曲线并清空原始参考线状态
- 保持FLAT_BANDS预设一致性优化未加载状态的体验

client/src/pages/EQPage.tsx

@@ -61,6 +61,7 @@ import {
   BAND_Q_MIN,
   DEFAULT_BANDS,
   FILTER_TYPES,
+  FLAT_BANDS,
   FLAT_PRESET_FILTERS,
   PEQ_PRESET_MAX,
 } from "./eq/eqConstants";
@@ -122,8 +123,8 @@ export default function EQPage() {
   const eqPageTitle = usePageTitleWithConnection("HP-EQ");
 
   const [bandsByMode, setBandsByMode] = useState<Record<"A" | "B", typeof DEFAULT_BANDS>>({
-    A: cloneBands(DEFAULT_BANDS),
-    B: cloneBands(DEFAULT_BANDS),
+    A: cloneBands(FLAT_BANDS),
+    B: cloneBands(FLAT_BANDS),
   });
   const [selectedBandByMode, setSelectedBandByMode] = useState<Record<"A" | "B", number>>({
     A: 0,
@@ -609,7 +610,7 @@ export default function EQPage() {
 
     const items = remote.peq ?? [];
     if (items.length === 0) {
-      setBandsForBothModes(DEFAULT_BANDS);
+      setBandsForBothModes(FLAT_BANDS);
       setSelectedBandByMode({ A: 0, B: 0 });
       return;
     }
@@ -1013,7 +1014,7 @@ export default function EQPage() {
             setHeadphoneModels([]);
             setPeqItems([]);
             selectHeadphone(0, "");
-            setBandsForBothModes(DEFAULT_BANDS);
+            setBandsForBothModes(FLAT_BANDS);
             setSelectedBandByMode({ A: 0, B: 0 });
             setCurrentRawCurve(null);
           }
@@ -1061,7 +1062,14 @@ export default function EQPage() {
   // 切换耳机型号后，从 peqItems 加载该型号的 filters（暂停一次上报避免错写）
   useEffect(() => {
     const peq = peqItems[headphoneIdx];
-    if (!peq) return;
+    if (!peq) {
+      // 列表为空（如设备端删光全部预设）：恢复平直曲线并清空 Raw 参考线
+      setBandsForBothModes(FLAT_BANDS);
+      setSelectedBandByMode({ A: 0, B: 0 });
+      setCurrentRawCurve(null);
+      setRawCurveLoading(false);
+      return;
+    }
     const nextBands = normalizeFiltersFromPeq(peq);
     if (!nextBands.length) return;
     syncingHeadphoneRef.current = true;

client/src/pages/eq/eqConstants.ts

@@ -36,6 +36,20 @@ export const DEFAULT_BANDS: EqBand[] = [
   { freq: 10000, gain: 0, q: 1.41, type: "HSHELF", enabled: true },
 ];
 
+/** Flat bands：无预设/未加载时展示的平直曲线（10 个 gain=0 的 PEAK） */
+export const FLAT_BANDS: EqBand[] = [
+  { freq: 80, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 150, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 350, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 750, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 1500, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 3000, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 6000, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 10000, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 14000, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+  { freq: 18000, gain: 0, q: 1.41, type: "PEAK", enabled: true },
+];
+
 export const FLAT_PRESET_FILTERS: PeqFilter[] = [
   { type: 4, fc: 80, gain: 0, q: 0.1 },
   { type: 4, fc: 150, gain: 0, q: 0.1 },