dsp/: C++ skeleton with working FFT/WOLA STFT

- Cooley-Tukey radix-2 FFT (forward + inverse with /N normalization)
- WOLA STFT/ISTFT with Hann window (nfft=2048, hop=512)
- WAV16 read + WAV24 write (fixed aliasing bug in read)
- Fixed in-place processing bug (separate input/output buffers)
- Biquad filter (peak/shelf/reject)
- Peak detector skeleton
- MS encode/decode (M8 stereo)
- Harness: WAV16 → STFT → WAV24 passthrough verified non-zero output

Verified: burst500.wav passthrough produces output RMS=0.0678

dsp/detect.hpp

@@ -0,0 +1,27 @@
+#pragma once
+#include <cstddef>
+#include <cstdint>
+#include <complex>
+
+struct Peak {
+    size_t bin;
+    float freq;
+    float magnitude;
+    float reduction;
+};
+
+class Detector {
+public:
+    Detector();
+    void setParams(float sharpness, float selectivity, float depth);
+    size_t detectPeaks(const std::complex<double>* spectrum, size_t n,
+                      float sample_rate, Peak* peaks, size_t max_peaks);
+    
+private:
+    float sharpness_;
+    float selectivity_;
+    float depth_;
+    
+    float computeReduction(float magnitude, float freq);
+};
+