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/PluginEditor.h

@@ -0,0 +1,52 @@
+#pragma once
+#include <JuceHeader.h>
+#include "PluginProcessor.h"
+#include "LookAndFeel.h"
+#include "EQCurveDisplay.h"
+#include "NodeParameterPanel.h"
+
+class InstaLPEQEditor : public juce::AudioProcessorEditor,
+                         private juce::Timer,
+                         private EQCurveDisplay::Listener,
+                         private NodeParameterPanel::Listener
+{
+public:
+    explicit InstaLPEQEditor (InstaLPEQProcessor& p);
+    ~InstaLPEQEditor() override;
+
+    void paint (juce::Graphics& g) override;
+    void resized() override;
+
+private:
+    void timerCallback() override;
+
+    // EQCurveDisplay::Listener
+    void bandAdded (int index, float freq, float gainDb) override;
+    void bandRemoved (int index) override;
+    void bandChanged (int index, const EQBand& band) override;
+    void selectedBandChanged (int index) override;
+
+    // NodeParameterPanel::Listener
+    void nodeParameterChanged (int bandIndex, const EQBand& band) override;
+    void nodeDeleteRequested (int bandIndex) override;
+
+    void syncDisplayFromProcessor();
+
+    InstaLPEQProcessor& processor;
+    InstaLPEQLookAndFeel customLookAndFeel;
+
+    EQCurveDisplay curveDisplay;
+    NodeParameterPanel nodePanel;
+
+    juce::Label titleLabel { {}, "INSTALPEQ" };
+    juce::Label versionLabel { {}, "v1.0" };
+    juce::ToggleButton bypassToggle;
+    juce::Label bypassLabel { {}, "BYPASS" };
+
+    juce::Slider masterGainSlider;
+    juce::Label masterGainLabel { {}, "MASTER" };
+
+    juce::ComponentBoundsConstrainer constrainer;
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (InstaLPEQEditor)
+};