Initial release — InstaShadow mastering compressor v1.0

Dual-stage compressor (optical + VCA) with output transformer saturation.
- Port-Hamiltonian T4B opto-cell model with implicit trapezoidal integration
- Feed-forward VCA with 7 ratios, 6 attack/release presets, Dual release mode
- 3 transformer types (Nickel/Iron/Steel) with 4x oversampled waveshaping
- Analog-style needle VU meters, horizontal GR meters
- Sidechain HPF, stereo link, independent section bypass
- Full state save/restore, CI/CD for Windows/macOS/Linux

Source/VCACompressor.h

@@ -0,0 +1,41 @@
+#pragma once
+#include <cmath>
+#include <algorithm>
+
+class VCACompressor
+{
+public:
+    VCACompressor();
+
+    void prepare (double sampleRate);
+    void reset();
+
+    // Process one sample: sidechainDb = input level in dB
+    // Returns gain in linear scale (0..1)
+    float processSample (float sidechainDb, float thresholdDb, float ratio,
+                         float attackSec, float releaseSec, bool dualRelease);
+
+    float getGainReductionDb() const { return currentGrDb; }
+
+private:
+    double sr = 44100.0;
+
+    // Gain smoothing state (dB domain)
+    double smoothedGrDb = 0.0;
+
+    // Dual release state
+    double dualFastEnv = 0.0;    // fast release envelope
+    double dualSlowEnv = 0.0;    // slow release envelope
+    bool wasCompressing = false;
+
+    float currentGrDb = 0.0f;
+
+    // Soft-knee width
+    static constexpr float kneeWidthDb = 6.0f;
+
+    // Gain computer: returns desired GR in dB (negative value)
+    float computeGainReduction (float inputDb, float thresholdDb, float ratio) const;
+
+    // Coefficient helpers
+    double makeCoeff (double timeSec) const;
+};