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/GRMeter.h

@@ -0,0 +1,59 @@
+#pragma once
+#include <JuceHeader.h>
+
+class GRMeter : public juce::Component
+{
+public:
+    void setGainReduction (float grDb)
+    {
+        float clamped = juce::jlimit (-30.0f, 0.0f, grDb);
+        float normalised = -clamped / 30.0f;
+        currentGr = std::max (normalised, currentGr * 0.92f);
+        if (normalised > peakGr) peakGr = normalised;
+        else peakGr *= 0.998f;
+        repaint();
+    }
+
+    void setBarColour (juce::Colour c) { barColour = c; }
+    void setLabel (const juce::String& text) { label = text; }
+
+    void paint (juce::Graphics& g) override
+    {
+        auto bounds = getLocalBounds().toFloat().reduced (1);
+
+        // Background
+        g.setColour (juce::Colour (0xff111122));
+        g.fillRoundedRectangle (bounds, 2.0f);
+
+        // GR bar (fills from right to left)
+        float w = bounds.getWidth() * currentGr;
+        auto filled = bounds.withLeft (bounds.getRight() - w);
+        g.setColour (barColour);
+        g.fillRoundedRectangle (filled, 2.0f);
+
+        // Peak hold line
+        if (peakGr > 0.01f)
+        {
+            float peakX = bounds.getRight() - bounds.getWidth() * peakGr;
+            g.setColour (juce::Colours::white.withAlpha (0.8f));
+            g.fillRect (peakX, bounds.getY(), 1.5f, bounds.getHeight());
+        }
+
+        // Label
+        g.setColour (juce::Colour (0xffe0e0e0).withAlpha (0.7f));
+        g.setFont (11.0f);
+        g.drawText (label, bounds.reduced (4, 0), juce::Justification::centredLeft);
+
+        // dB readout
+        float dbVal = -currentGr * 30.0f;
+        if (currentGr > 0.001f)
+            g.drawText (juce::String (dbVal, 1) + " dB", bounds.reduced (4, 0),
+                        juce::Justification::centredRight);
+    }
+
+private:
+    float currentGr = 0.0f;
+    float peakGr = 0.0f;
+    juce::Colour barColour { 0xffff8833 };
+    juce::String label;
+};