Initial release — InstaGrain granular synthesizer v1.0

8-voice polyphonic granular synth (VST3/AU/LV2) with:
- 128 grain pool per voice, Hann windowing, linear interpolation
- Root note selector, sample rate correction, sustain pedal (CC64)
- Scatter controls, direction modes (Fwd/Rev/PingPong), freeze
- ADSR envelope, global filter (LP/HP/BP), reverb
- Waveform display with grain visualization
- Drag & drop sample loading, full state save/restore
- CI/CD for Windows/macOS/Linux

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

Source/PluginEditor.h

@@ -0,0 +1,58 @@
+#pragma once
+#include <JuceHeader.h>
+#include "PluginProcessor.h"
+#include "LookAndFeel.h"
+#include "WaveformDisplay.h"
+#include "GrainControlPanel.h"
+#include "ScatterPanel.h"
+#include "EnvelopePanel.h"
+#include "EffectsPanel.h"
+#include "MasterPanel.h"
+
+static constexpr const char* kInstaGrainVersion = "v1.0";
+
+class InstaGrainEditor : public juce::AudioProcessorEditor,
+                          public juce::FileDragAndDropTarget,
+                          public juce::Timer
+{
+public:
+    explicit InstaGrainEditor (InstaGrainProcessor&);
+    ~InstaGrainEditor() override;
+
+    void paint (juce::Graphics&) override;
+    void resized() override;
+
+    // FileDragAndDropTarget
+    bool isInterestedInFileDrag (const juce::StringArray& files) override;
+    void filesDropped (const juce::StringArray& files, int x, int y) override;
+
+    // Timer
+    void timerCallback() override;
+
+private:
+    InstaGrainProcessor& processor;
+    InstaGrainLookAndFeel lookAndFeel;
+
+    // Top bar
+    juce::Label titleLabel;
+    juce::Label versionLabel;
+    juce::TextButton loadButton { "LOAD SAMPLE" };
+    juce::ToggleButton bypassButton;
+    juce::Label bypassLabel;
+
+    // Panels
+    WaveformDisplay waveformDisplay;
+    GrainControlPanel grainPanel;
+    ScatterPanel scatterPanel;
+    EnvelopePanel envelopePanel;
+    EffectsPanel effectsPanel;
+    MasterPanel masterPanel;
+
+    std::unique_ptr<juce::FileChooser> fileChooser;
+
+    void loadSampleFile (const juce::File& file);
+    void syncKnobsToEngine();
+    void syncEngineFromKnobs();
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (InstaGrainEditor)
+};