Implement community forum integration in CommunityPage; update BottomNav to conditionally display community tab based on screen size. Add new audio processing function for combined PEQ magnitude calculation in peqAudio.

client/src/lib/peqAudio.ts

@@ -359,6 +359,26 @@ export function computePeqMagnitudeDb(bands: PeqBandForResponse[], fs: number):
   return getFreqznList(list, fs, f);
 }
 
+/**
+ * 级联后总幅度（dB）在某一频率上的值，与 {@link computePeqMagnitudeDb} / 黄线 EQ 曲线同源。
+ * 用于把 10 个拖拽点画在曲线上（曲线为各带合成响应，不能再用单带的 gain 参数当纵坐标）。
+ */
+export function sampleCombinedPeqMagnitudeDb(
+  bands: PeqBandForResponse[],
+  freq: number,
+  fs: number = 48000,
+): number {
+  const fc = Math.max(20, Math.min(20000, freq));
+  const list: Coeff[] = [];
+  bands.forEach((b) => {
+    if (!b.enabled) return;
+    list.push(getSectionsMatrix(b.gain, b.freq, b.q, getFilterType(b.type), false, fs));
+  });
+  if (list.length === 0) return 0;
+  const out = getFreqznList(list, fs, [fc]);
+  return out[0] ?? 0;
+}
+
 export type PeqSvgCurveData = {
   points: Array<{ x: number; y: number; gainDb: number; freq: number }>;
   pathD: string;