Initial commit: InstaLPEQ linear phase EQ plugin

Full-featured linear phase EQ with interactive graphical curve display.
FIR-based processing (8192-tap), 8 parametric bands, multi-platform
CI/CD (Windows/macOS/Linux), InstaDrums visual style.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Source/EQCurveDisplay.h

@@ -0,0 +1,71 @@
+#pragma once
+#include <JuceHeader.h>
+#include "EQBand.h"
+
+class EQCurveDisplay : public juce::Component
+{
+public:
+    struct Listener
+    {
+        virtual ~Listener() = default;
+        virtual void bandAdded (int index, float freq, float gainDb) = 0;
+        virtual void bandRemoved (int index) = 0;
+        virtual void bandChanged (int index, const EQBand& band) = 0;
+        virtual void selectedBandChanged (int index) = 0;
+    };
+
+    EQCurveDisplay();
+
+    void setListener (Listener* l) { listener = l; }
+    void setBands (const std::vector<EQBand>& bands);
+    void setMagnitudeResponse (const std::vector<float>& magnitudesDb, double sampleRate, int fftSize);
+    int getSelectedBandIndex() const { return selectedBand; }
+    void setSelectedBand (int index);
+
+    void paint (juce::Graphics& g) override;
+    void mouseDown (const juce::MouseEvent& e) override;
+    void mouseDrag (const juce::MouseEvent& e) override;
+    void mouseUp (const juce::MouseEvent& e) override;
+    void mouseDoubleClick (const juce::MouseEvent& e) override;
+    void mouseWheelMove (const juce::MouseEvent& e, const juce::MouseWheelDetails& w) override;
+
+private:
+    std::vector<EQBand> bands;
+    std::vector<float> magnitudeResponseDb;
+    double responseSampleRate = 44100.0;
+    int responseFftSize = 8192;
+    int selectedBand = -1;
+    int draggedBand = -1;
+    Listener* listener = nullptr;
+
+    static constexpr float minFreq = 20.0f;
+    static constexpr float maxFreq = 20000.0f;
+    static constexpr float minDb = -24.0f;
+    static constexpr float maxDb = 24.0f;
+
+    // Node colours (8 distinct colours for up to 8 bands)
+    static inline const juce::Colour nodeColours[8] = {
+        juce::Colour (0xffff6644),  // orange-red
+        juce::Colour (0xff44bbff),  // sky blue
+        juce::Colour (0xffff44aa),  // pink
+        juce::Colour (0xff44ff88),  // green
+        juce::Colour (0xffffff44),  // yellow
+        juce::Colour (0xffaa44ff),  // purple
+        juce::Colour (0xff44ffff),  // cyan
+        juce::Colour (0xffff8844),  // orange
+    };
+
+    juce::Rectangle<float> getPlotArea() const;
+    float freqToX (float freq) const;
+    float xToFreq (float x) const;
+    float dbToY (float db) const;
+    float yToDb (float y) const;
+
+    void drawGrid (juce::Graphics& g);
+    void drawResponseCurve (juce::Graphics& g);
+    void drawPerBandCurves (juce::Graphics& g);
+    void drawNodes (juce::Graphics& g);
+    int findNodeAt (float x, float y, float radius = 14.0f) const;
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (EQCurveDisplay)
+};