feat: complete Phase 10.3 - master metering with peak/RMS display

Added comprehensive master output level monitoring:
- Created MasterMeter component with dual vertical bars (peak + RMS)
- Implemented real-time level monitoring in useMultiTrackPlayer hook
- Added master analyser node connected to audio output
- Displays color-coded levels (green/yellow/red) based on dB thresholds
- Shows numerical dB readouts for both peak and RMS
- Includes clickable clip indicator with reset functionality
- Integrated into PlaybackControls next to master volume

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/controls/MasterMeter.tsx

@@ -0,0 +1,120 @@
+'use client';
+
+import * as React from 'react';
+
+export interface MasterMeterProps {
+  /** Peak level (0-1) */
+  peakLevel: number;
+  /** RMS level (0-1) */
+  rmsLevel: number;
+  /** Whether clipping has occurred */
+  isClipping: boolean;
+  /** Callback to reset clip indicator */
+  onResetClip?: () => void;
+}
+
+export function MasterMeter({
+  peakLevel,
+  rmsLevel,
+  isClipping,
+  onResetClip,
+}: MasterMeterProps) {
+  // Convert linear 0-1 to dB scale for display
+  const linearToDb = (linear: number): number => {
+    if (linear === 0) return -60;
+    const db = 20 * Math.log10(linear);
+    return Math.max(-60, Math.min(0, db));
+  };
+
+  const peakDb = linearToDb(peakLevel);
+  const rmsDb = linearToDb(rmsLevel);
+
+  // Calculate bar heights (0-100%)
+  const peakHeight = ((peakDb + 60) / 60) * 100;
+  const rmsHeight = ((rmsDb + 60) / 60) * 100;
+
+  return (
+    <div className="flex items-center gap-2 px-3 py-2 bg-muted/30 rounded-md border border-border/50">
+      {/* Clip Indicator */}
+      <button
+        onClick={onResetClip}
+        className={`w-6 h-6 rounded-sm border transition-colors ${
+          isClipping
+            ? 'bg-red-500 border-red-600 shadow-lg shadow-red-500/50'
+            : 'bg-muted border-border/50'
+        }`}
+        title={isClipping ? 'Click to reset clip indicator' : 'No clipping'}
+      >
+        <span className="text-[10px] font-bold text-white">C</span>
+      </button>
+
+      {/* Meters */}
+      <div className="flex gap-1">
+        {/* Peak Meter (Left) */}
+        <div className="w-6 h-24 bg-background/50 rounded-sm relative overflow-hidden border border-border/50">
+          <div className="absolute bottom-0 left-0 right-0 transition-all duration-75 ease-out"
+               style={{ height: `${Math.max(0, Math.min(100, peakHeight))}%` }}>
+            <div className={`w-full h-full ${
+              peakDb > -3 ? 'bg-red-500' :
+              peakDb > -6 ? 'bg-yellow-500' :
+              'bg-green-500'
+            }`} />
+          </div>
+          {/* dB markers */}
+          <div className="absolute inset-0 pointer-events-none">
+            <div className="absolute top-0 left-0 right-0 h-px bg-red-500/30" title="0 dB" />
+            <div className="absolute top-[5%] left-0 right-0 h-px bg-yellow-500/20" title="-3 dB" />
+            <div className="absolute top-[10%] left-0 right-0 h-px bg-border/20" title="-6 dB" />
+            <div className="absolute top-[25%] left-0 right-0 h-px bg-border/20" title="-12 dB" />
+            <div className="absolute top-[50%] left-0 right-0 h-px bg-border/20" title="-18 dB" />
+          </div>
+        </div>
+
+        {/* RMS Meter (Right) */}
+        <div className="w-6 h-24 bg-background/50 rounded-sm relative overflow-hidden border border-border/50">
+          <div className="absolute bottom-0 left-0 right-0 transition-all duration-150 ease-out"
+               style={{ height: `${Math.max(0, Math.min(100, rmsHeight))}%` }}>
+            <div className={`w-full h-full ${
+              rmsDb > -3 ? 'bg-red-400' :
+              rmsDb > -6 ? 'bg-yellow-400' :
+              'bg-green-400'
+            }`} />
+          </div>
+          {/* dB markers */}
+          <div className="absolute inset-0 pointer-events-none">
+            <div className="absolute top-0 left-0 right-0 h-px bg-red-500/30" />
+            <div className="absolute top-[5%] left-0 right-0 h-px bg-yellow-500/20" />
+            <div className="absolute top-[10%] left-0 right-0 h-px bg-border/20" />
+            <div className="absolute top-[25%] left-0 right-0 h-px bg-border/20" />
+            <div className="absolute top-[50%] left-0 right-0 h-px bg-border/20" />
+          </div>
+        </div>
+      </div>
+
+      {/* Labels and Values */}
+      <div className="flex flex-col text-[10px] font-mono">
+        <div className="flex items-center gap-1">
+          <span className="text-muted-foreground w-6">PK:</span>
+          <span className={`w-12 text-right ${
+            peakDb > -3 ? 'text-red-500' :
+            peakDb > -6 ? 'text-yellow-500' :
+            'text-green-500'
+          }`}>
+            {peakDb > -60 ? `${peakDb.toFixed(1)}` : '-∞'}
+          </span>
+        </div>
+        <div className="flex items-center gap-1">
+          <span className="text-muted-foreground w-6">RM:</span>
+          <span className={`w-12 text-right ${
+            rmsDb > -3 ? 'text-red-400' :
+            rmsDb > -6 ? 'text-yellow-400' :
+            'text-green-400'
+          }`}>
+            {rmsDb > -60 ? `${rmsDb.toFixed(1)}` : '-∞'}
+          </span>
+        </div>
+        <div className="text-muted-foreground text-center mt-0.5">dB</div>
+      </div>
+    </div>
+  );
+}