Add Psytrance Visualizer macOS app with Metal rendering

A complete audio-reactive visualizer for psytrance music featuring:

Audio Analysis (DSPEngine):
- FFT spectrum analysis via Accelerate/vDSP
- 64-band Mel spectrogram
- Sub-bass energy extraction (<100Hz)
- Automatic sidechain pump detection
- Harmonic-to-Noise ratio (HNR) calculation
- Peak/transient detection

8 Visualization Modes (Metal Shaders):
1. FFT Classic - Frequency spectrum bars with glow
2. Mel Spectrogram - Waterfall display
3. Sub-Bass - Pulsating rings
4. Sidechain Pump - Breathing zoom effect
5. Harmonic/Noise - Geometric vs chaotic particles
6. Mandelbrot - Audio-reactive fractal zoom
7. Tunnel Warp - Infinite tunnel with distortion
8. DMT Geometry - Sacred geometry patterns

Features:
- Selectable audio input device (BlackHole support)
- Configurable buffer size (512/1024)
- Reactivity slider for visual intensity
- Auto-hiding control panel
- Fullscreen support with keyboard shortcuts (1-8, F, ESC)
- Persistent settings via UserDefaults
- Psytrance-inspired neon/UV color palette

PsytranceVisualizer/UI/VisualizerView.swift

@@ -0,0 +1,122 @@
+//
+//  VisualizerView.swift
+//  PsytranceVisualizer
+//
+//  MTKView subclass for rendering visualizations
+//
+
+import MetalKit
+import Combine
+
+/// MTKView subclass that displays audio-reactive visualizations
+final class VisualizerView: MTKView {
+    // MARK: - Properties
+
+    private var renderer: MetalRenderer?
+    private var cancellables = Set<AnyCancellable>()
+
+    // MARK: - Initialization
+
+    init() {
+        // Get default Metal device
+        guard let device = MTLCreateSystemDefaultDevice() else {
+            fatalError("Metal is not supported on this device")
+        }
+
+        super.init(frame: .zero, device: device)
+
+        configure()
+        setupRenderer()
+    }
+
+    required init(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    // MARK: - Configuration
+
+    private func configure() {
+        // Background color
+        clearColor = MTLClearColor(red: 0, green: 0, blue: 0, alpha: 1)
+
+        // Color format
+        colorPixelFormat = .bgra8Unorm
+
+        // Enable display link for smooth rendering
+        isPaused = false
+        enableSetNeedsDisplay = false
+
+        // Use display refresh rate
+        preferredFramesPerSecond = 120 // Will cap to display refresh
+
+        // Layer configuration
+        layer?.isOpaque = true
+
+        // Allow high DPI
+        layer?.contentsScale = NSScreen.main?.backingScaleFactor ?? 2.0
+    }
+
+    private func setupRenderer() {
+        guard let device = device else { return }
+
+        renderer = MetalRenderer(device: device)
+        delegate = renderer
+
+        // Initial size update
+        if let renderer = renderer {
+            let size = drawableSize
+            renderer.mtkView(self, drawableSizeWillChange: size)
+        }
+    }
+
+    // MARK: - Public Methods
+
+    /// Returns the Metal renderer
+    func getRenderer() -> MetalRenderer? {
+        return renderer
+    }
+
+    /// Updates audio data for visualization
+    func updateAudioData(_ data: AudioAnalysisData) {
+        renderer?.updateAudioData(data)
+    }
+
+    /// Sets the visualization mode
+    func setVisualizationMode(_ mode: VisualizationMode) {
+        renderer?.setVisualizationMode(mode)
+    }
+
+    /// Sets reactivity value
+    func setReactivity(_ value: Float) {
+        renderer?.setReactivity(value)
+    }
+
+    /// Gets current visualization mode
+    var currentMode: VisualizationMode {
+        renderer?.currentMode ?? .fftClassic
+    }
+}
+
+// MARK: - SwiftUI Bridge
+
+#if canImport(SwiftUI)
+import SwiftUI
+
+/// SwiftUI wrapper for VisualizerView
+struct VisualizerViewRepresentable: NSViewRepresentable {
+    @Binding var audioData: AudioAnalysisData
+    @Binding var mode: VisualizationMode
+    @Binding var reactivity: Float
+
+    func makeNSView(context: Context) -> VisualizerView {
+        let view = VisualizerView()
+        return view
+    }
+
+    func updateNSView(_ nsView: VisualizerView, context: Context) {
+        nsView.updateAudioData(audioData)
+        nsView.setVisualizationMode(mode)
+        nsView.setReactivity(reactivity)
+    }
+}
+#endif