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/Rendering/Shaders/MelSpectrogramShader.metal

@@ -0,0 +1,95 @@
+//
+//  MelSpectrogramShader.metal
+//  PsytranceVisualizer
+//
+//  Mel spectrogram with scrolling waterfall display
+//
+
+#include <metal_stdlib>
+using namespace metal;
+
+#include "Common.metal"
+
+fragment float4 melSpectrogramFragment(
+    VertexOut in [[stage_in]],
+    constant ShaderUniforms& uniforms [[buffer(0)]],
+    constant float* fftData [[buffer(1)]],
+    constant float* melData [[buffer(2)]],
+    constant float* historyData [[buffer(3)]]
+) {
+    float2 uv = in.uv;
+    float time = uniforms.time;
+    float reactivity = uniforms.reactivity;
+
+    // Configuration
+    const int numBands = 64;
+    const int historyLength = 128;
+
+    // Map UV to mel band and history position
+    int bandIndex = int(uv.x * float(numBands));
+    bandIndex = clamp(bandIndex, 0, numBands - 1);
+
+    // Scrolling effect - newer data at bottom
+    float scrollOffset = fract(time * 0.5); // Scroll speed
+    float yPos = fract(uv.y + scrollOffset);
+
+    // Get mel magnitude
+    float magnitude = melData[bandIndex];
+    magnitude = magnitude * (0.5 + reactivity * 1.5);
+    magnitude = clamp(magnitude, 0.0, 1.0);
+
+    // Create waterfall effect using history
+    int historyIndex = int(yPos * float(historyLength));
+    historyIndex = clamp(historyIndex, 0, historyLength - 1);
+
+    // Combine current and historical data for waterfall
+    float historicalValue = historyData[historyIndex];
+
+    // Blend between current magnitude and position-based intensity
+    float intensity = magnitude;
+
+    // Add some variance based on band position
+    float bandPhase = float(bandIndex) / float(numBands);
+    intensity *= 0.8 + 0.2 * sin(bandPhase * 6.28318 + time);
+
+    // Apply fade for older data (top of screen)
+    float ageFade = 1.0 - uv.y * 0.3;
+    intensity *= ageFade;
+
+    // Generate color using heatmap
+    float3 color = heatmap(intensity);
+
+    // Add frequency-dependent hue shift
+    float hueShift = bandPhase * 0.3;
+    color = psytrancePalette(intensity + hueShift, time);
+
+    // Modulate by actual intensity
+    color *= 0.3 + intensity * 0.7;
+
+    // Add grid lines for visual reference
+    float gridX = abs(fract(uv.x * float(numBands)) - 0.5) * 2.0;
+    float gridY = abs(fract(uv.y * 16.0) - 0.5) * 2.0;
+
+    float gridLine = smoothstep(0.95, 1.0, gridX) + smoothstep(0.95, 1.0, gridY);
+    gridLine *= 0.1;
+
+    color += float3(gridLine) * uvViolet;
+
+    // Add glow on high energy
+    if (intensity > 0.7) {
+        float glow = (intensity - 0.7) / 0.3;
+        color = addGlow(color, glow * 0.5, neonCyan);
+    }
+
+    // Peak flash
+    if (uniforms.isPeak > 0.5) {
+        color += neonMagenta * uniforms.peakIntensity * 0.15;
+    }
+
+    // Sub-bass emphasis on lower bands
+    if (bandIndex < 8) {
+        color += uvViolet * uniforms.subBassEnergy * 0.3;
+    }
+
+    return float4(color, 1.0);
+}