feat: add PipeWire muter functionality and service files for Sendspin audio player

internal/pipewire/nodes.go

@@ -62,6 +62,32 @@ func listAllNodes() ([]Node, error) {
 	return nodes, nil
 }
 
+// FindNodeIDByName scans every PipeWire node (not just Audio/*) and returns
+// the numeric ID of the first one whose node.name matches. Used by the
+// loopback muter, where the target may be a stream/loopback rather than a
+// sink/source. Returns -1 with an error when no match is found.
+func FindNodeIDByName(name string) (int, error) {
+	out, err := exec.Command("pw-dump").Output()
+	if err != nil {
+		return -1, fmt.Errorf("pw-dump: %w", err)
+	}
+
+	var objects []pwObject
+	if err := json.Unmarshal(out, &objects); err != nil {
+		return -1, fmt.Errorf("parse pw-dump: %w", err)
+	}
+
+	for _, o := range objects {
+		if o.Type != "PipeWire:Interface:Node" {
+			continue
+		}
+		if o.Info.Props.NodeName == name {
+			return o.ID, nil
+		}
+	}
+	return -1, fmt.Errorf("no PipeWire node with node.name=%q", name)
+}
+
 func ListSinks() ([]Node, error) {
 	all, err := listAllNodes()
 	if err != nil {