feat: buffer/latency control + non-selectable node text

Buffer Control:
- GET /api/quantum - reads current graph quantum via pw-metadata
- POST /api/quantum {quantum:N} - sets quantum via pw-metadata
- Toolbar dropdown with presets: 32, 64, 128, 256, 512, 1024, 2048, 4096
- Loads current quantum on startup

Text Selection Fix:
- Added user-select: none to wrap and canvas CSS
- Node text no longer gets selected when dragging

frontend/src/components/GraphCanvas.svelte

@@ -13,6 +13,7 @@
     saveProfile, loadProfile, deleteProfile,
     setNodeVolume, setNodeMute,
     createNullSink, createLoopback, loadModule,
+    getQuantum, setQuantum,
   } from '../lib/stores';
   import type { Node, Port, Link } from '../lib/types';
 
@@ -50,6 +51,7 @@
 
   // Positions
   let nodePositions = $state<Record<string, { x: number; y: number }>>({});
+  let currentQuantum = $state(0);
   const POS_KEY = 'pwweb_positions';
 
   function loadPositions() {
@@ -420,7 +422,7 @@
     }
   }
 
-  onMount(() => { initGraph(); loadPositions(); });
+  onMount(() => { initGraph(); loadPositions(); getQuantum().then(q => { currentQuantum = q; }); });
   onDestroy(() => { destroyGraph(); });
 </script>
 
@@ -460,6 +462,15 @@
     <button onclick={() => { showRuleDialog = !showRuleDialog; showHideDialog = false; showMergeDialog = false; showProfileDialog = false; }} title="Manage patchbay rules">Rules</button>
     <button onclick={() => { showProfileDialog = !showProfileDialog; showHideDialog = false; showMergeDialog = false; showRuleDialog = false; }} title="Save/load profiles">Profiles</button>
     <button onclick={() => { showVirtualMenu = !showVirtualMenu; showHideDialog = false; showMergeDialog = false; showProfileDialog = false; showRuleDialog = false; }} title="Add virtual device">+ Add</button>
+    <span class="sep"></span>
+    <label class="quantum-label">Buffer:
+      <select class="quantum-select" onchange={(e) => { const q = Number((e.target as HTMLSelectElement).value); if (q > 0) { currentQuantum = q; setQuantum(q); } }}>
+        <option value="0" selected={currentQuantum === 0}>default</option>
+        {#each [32, 64, 128, 256, 512, 1024, 2048, 4096] as q}
+          <option value={q} selected={currentQuantum === q}>{q}</option>
+        {/each}
+      </select>
+    </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>
   </div>
@@ -821,8 +832,8 @@
 </div>
 
 <style>
-  .wrap { width: 100%; height: 100vh; background: #14141e; position: relative; overflow: hidden; }
-  .canvas { width: 100%; height: 100%; display: block; cursor: default; position: absolute; top: 0; left: 0; z-index: 1; }
+  .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; }
 
   .toolbar {
     position: absolute; top: 0; left: 0; right: 0; z-index: 10;
@@ -859,6 +870,12 @@
   .toolbar button:hover, .toggle:hover { background: #3a3a4e; }
   .toggle.active { background: #1a3a2a; border-color: #4a9; color: #6c9; }
 
+  .quantum-label { font-size: 10px; color: #888; display: flex; align-items: center; gap: 4px; }
+  .quantum-select {
+    padding: 1px 4px; background: #1a1a2e; border: 1px solid #444;
+    color: #aaa; font-size: 10px; border-radius: 3px; font-family: monospace;
+    cursor: pointer;
+  }
   .stats { margin-left: auto; color: #555; }
 
   /* Context menu */

frontend/src/lib/stores.ts

@@ -441,4 +441,25 @@ export async function unloadModule(moduleId: number) {
   }
 }
 
+// Quantum (buffer size) control
+export async function getQuantum(): Promise<number> {
+  try {
+    const res = await fetch('/api/quantum');
+    const data = await res.json();
+    return data.quantum || 0;
+  } catch { return 0; }
+}
+
+export async function setQuantum(quantum: number) {
+  try {
+    await fetch('/api/quantum', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ quantum }),
+    });
+  } catch (e) {
+    console.error('[api] set-quantum failed:', e);
+  }
+}
+
 export { connectPorts, disconnectPorts };