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/PluginProcessor.h

@@ -0,0 +1,64 @@
+#pragma once
+#include <JuceHeader.h>
+#include "EQBand.h"
+#include "FIREngine.h"
+
+class InstaLPEQProcessor : public juce::AudioProcessor
+{
+public:
+    static constexpr int maxBands = 8;
+
+    InstaLPEQProcessor();
+    ~InstaLPEQProcessor() override;
+
+    void prepareToPlay (double sampleRate, int samplesPerBlock) override;
+    void releaseResources() override;
+    void processBlock (juce::AudioBuffer<float>&, juce::MidiBuffer&) override;
+
+    juce::AudioProcessorEditor* createEditor() override;
+    bool hasEditor() const override { return true; }
+
+    const juce::String getName() const override { return JucePlugin_Name; }
+    bool acceptsMidi() const override { return false; }
+    bool producesMidi() const override { return false; }
+    bool isBusesLayoutSupported (const BusesLayout& layouts) const override;
+    double getTailLengthSeconds() const override { return 0.0; }
+
+    int getNumPrograms() override { return 1; }
+    int getCurrentProgram() override { return 0; }
+    void setCurrentProgram (int) override {}
+    const juce::String getProgramName (int) override { return {}; }
+    void changeProgramName (int, const juce::String&) override {}
+
+    void getStateInformation (juce::MemoryBlock& destData) override;
+    void setStateInformation (const void* data, int sizeInBytes) override;
+
+    // Band management (called from GUI thread)
+    std::vector<EQBand> getBands() const;
+    void setBand (int index, const EQBand& band);
+    void addBand (float freq, float gainDb);
+    void removeBand (int index);
+    int getNumBands() const;
+
+    // Settings
+    std::atomic<bool> bypassed { false };
+    std::atomic<float> masterGainDb { 0.0f };
+
+    FIREngine& getFIREngine() { return firEngine; }
+    double getCurrentSampleRate() const { return currentSampleRate; }
+
+private:
+    std::vector<EQBand> bands;
+    juce::SpinLock bandLock;
+
+    FIREngine firEngine;
+    juce::dsp::Convolution convolution;
+
+    double currentSampleRate = 44100.0;
+    int currentBlockSize = 512;
+    bool firLoaded = false;
+
+    void updateFIR();
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (InstaLPEQProcessor)
+};