feat: built-in volume management

- Volume slider on every node (green bar, draggable)
- Mute toggle button (M/m) on every node
- Backend: read volume/mute from PipeWire node props
- Backend: POST /api/volume {node_id, volume} to set volume
- Backend: POST /api/mute {node_id, mute} to toggle mute
- Graph JSON includes volume and mute fields per node
- Slider supports drag-to-adjust with mouse

frontend/src/lib/stores.ts

@@ -358,4 +358,29 @@ export function deleteProfile(name: string) {
   savePatchbayState();
 }
 
+// Volume control
+export async function setNodeVolume(nodeId: number, volume: number) {
+  try {
+    await fetch('/api/volume', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ node_id: nodeId, volume }),
+    });
+  } catch (e) {
+    console.error('[api] volume failed:', e);
+  }
+}
+
+export async function setNodeMute(nodeId: number, mute: boolean) {
+  try {
+    await fetch('/api/mute', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ node_id: nodeId, mute }),
+    });
+  } catch (e) {
+    console.error('[api] mute failed:', e);
+  }
+}
+
 export { connectPorts, disconnectPorts };