feat: graph region fix, toggle button, segmented VU meters

- Fix graph escaping toolbar: switch .wrap to flexbox + .toolbar to
  position:relative so the SVG canvas sits strictly below the toolbar
- Add "Graph" toggle button in toolbar to show/hide the canvas
- Replace thin 3px meter bar with 20-segment horizontal LED bar
  (10px tall, 1.5px gaps); green 0-75%, yellow 75-90%, red 90-100%

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

frontend/src/components/GraphCanvas.svelte

@@ -139,17 +139,20 @@
     return $patchbay.aliases?.[nd.name] || nd.nick || nd.name;
   }
 
-  // Level meter helpers
-  function meterDb(nodeId: number): number {
+  // Graph visibility toggle
+  let showGraph = $state(true);
+
+  // Level meter: returns how many of `total` segments should be lit
+  function meterSegs(nodeId: number, total: number): number {
     const p = $peaks[nodeId] ?? 0;
-    return p > 0 ? Math.max(-60, 20 * Math.log10(p)) : -60;
+    if (p <= 0) return 0;
+    const db = Math.max(-60, 20 * Math.log10(p));
+    return Math.round(Math.max(0, (db + 60) / 60) * total);
   }
-  function meterWidth(nodeId: number, barW: number): number {
-    return barW * Math.max(0, (meterDb(nodeId) + 60) / 60);
-  }
-  function meterColor(nodeId: number): string {
-    const db = meterDb(nodeId);
-    return db >= -3 ? '#c44' : db >= -12 ? '#ca4' : '#4a9';
+  // Segment color by position (0 = leftmost/quietest)
+  function segColor(i: number, total: number): string {
+    const pct = i / total;
+    return pct >= 0.90 ? '#c44' : pct >= 0.75 ? '#ca4' : '#4a9';
   }
 
   // Build computed layout
@@ -207,7 +210,7 @@
       const headerH = 22;
       const portH = 16;
       const maxPorts = Math.max(allInPorts.length, allOutPorts.length, 1);
-      const height = headerH + maxPorts * portH + 28; // 20 for volume slider + 8 for meter bar
+      const height = headerH + maxPorts * portH + 36; // 20 for volume slider + 16 for VU meter
       const width = 220;
 
       const portPositions = new Map<number, { x: number; y: number }>();
@@ -507,6 +510,8 @@
     </label>
 
     <span class="stats">{$nodes.length}N {$ports.length}P {$links.length}L {#if $patchbay.pinned_connections.length > 0}{$patchbay.pinned_connections.length}p{/if}</span>
+    <span class="sep"></span>
+    <button class="toggle" class:active={showGraph} onclick={() => showGraph = !showGraph} title="Show/hide graph canvas">Graph</button>
   </div>
 
   <!-- Virtual device dropdown -->
@@ -551,6 +556,7 @@
   {/if}
 
   <!-- svelte-ignore a11y_no_static_element_interactions -->
+  {#if showGraph}
   <svg
     bind:this={svgEl}
     viewBox="{viewBox.x} {viewBox.y} {viewBox.w} {viewBox.h}"
@@ -690,13 +696,22 @@
           {Math.round(Math.max(0, Math.min(1, nd.volume)) * 100)}%
         </text>
 
-        <!-- Level meter -->
-        <rect x={nd.x + 8} y={nd.y + nd.height - 6} width={nd.width - 16} height="3" rx="1" fill="#1a1a1a" />
-        <rect x={nd.x + 8} y={nd.y + nd.height - 6} width={meterWidth(nd.id, nd.width - 16)} height="3" rx="1" fill={meterColor(nd.id)} />
+        <!-- VU meter: 20 segmented LEDs -->
+        {#each Array(20) as _, i}
+          <rect
+            x={nd.x + 8 + i * ((nd.width - 16) / 20)}
+            y={nd.y + nd.height - 13}
+            width={(nd.width - 16) / 20 - 1.5}
+            height="10"
+            rx="1"
+            fill={i < meterSegs(nd.id, 20) ? segColor(i, 20) : '#1e1e28'}
+          />
+        {/each}
 
       </g>
     {/each}
   </svg>
+  {/if}
 
   <!-- Context menu -->
   {#if contextMenu}
@@ -908,11 +923,11 @@
 </div>
 
 <style>
-  .wrap { width: 100%; height: 100vh; background: #14141e; position: relative; overflow: hidden; user-select: none; -webkit-user-select: none; }
-  .canvas { width: 100%; height: 100%; display: block; cursor: default; position: absolute; top: 0; left: 0; z-index: 1; user-select: none; -webkit-user-select: none; }
+  .wrap { width: 100%; height: 100vh; background: #14141e; display: flex; flex-direction: column; position: relative; overflow: hidden; user-select: none; -webkit-user-select: none; }
+  .canvas { flex: 1; min-height: 0; width: 100%; display: block; cursor: default; z-index: 1; user-select: none; -webkit-user-select: none; }
 
   .toolbar {
-    position: absolute; top: 0; left: 0; right: 0; z-index: 10;
+    position: relative; flex-shrink: 0; z-index: 10;
     display: flex; align-items: center; gap: 6px;
     padding: 4px 10px;
     background: rgba(16, 16, 24, 0.97);