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/TransformerSaturation.h

@@ -0,0 +1,34 @@
+#pragma once
+#include <JuceHeader.h>
+
+class TransformerSaturation
+{
+public:
+    enum Type { Off = 0, Nickel = 1, Iron = 2, Steel = 3 };
+
+    TransformerSaturation();
+
+    void prepare (double sampleRate, int samplesPerBlock);
+    void reset();
+
+    // Process buffer in-place with 4x oversampling
+    void processBlock (juce::AudioBuffer<float>& buffer, Type type);
+
+private:
+    double sr = 44100.0;
+
+    // 4x oversampler (stereo)
+    juce::dsp::Oversampling<float> oversampler { 2, 2,
+        juce::dsp::Oversampling<float>::filterHalfBandPolyphaseIIR };
+
+    // Subtle tonestack (post-saturation)
+    juce::dsp::IIR::Filter<float> ironBoostL, ironBoostR;
+    juce::dsp::IIR::Filter<float> steelBoostL, steelBoostR;
+
+    // Simple pre-emphasis for frequency-dependent saturation
+    // Boost lows before waveshaper, compensate after
+    juce::dsp::IIR::Filter<float> preEmphL, preEmphR;
+    juce::dsp::IIR::Filter<float> deEmphL, deEmphR;
+
+    void setupPreEmphasis (double sampleRate, float boostDb);
+};