fix: move VU meter above volume controls to stop blocking mute button

Meter was at nd.height-13 overlapping the mute button (nd.height-17,
h=12). Moved to nd.height-35 so it sits in the dedicated extra space
above the control zone, leaving the bottom 22px fully clear.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/GraphCanvas.svelte

@@ -696,11 +696,11 @@
           {Math.round(Math.max(0, Math.min(1, nd.volume)) * 100)}%
         </text>
 
-        <!-- VU meter: 20 segmented LEDs -->
+        <!-- VU meter: 20 segmented LEDs (above the volume/mute controls) -->
         {#each Array(20) as _, i}
           <rect
             x={nd.x + 8 + i * ((nd.width - 16) / 20)}
-            y={nd.y + nd.height - 13}
+            y={nd.y + nd.height - 35}
             width={(nd.width - 16) / 20 - 1.5}
             height="10"
             rx="1"