fix: name the audio device in diagnostics instead of quoting its GUID

The watchdog fired exactly as intended and said:

  no audio at all from "{0.0.1.00000000}.{6a27abfd-f277-496b-b6f1-f92ec284c636}"

which tells the operator nothing they can act on. "DAX RX 1 (FlexRadio DAX)"
points straight at the DAX panel.

Endpoint ids are what gets CONFIGURED and stored, so they are what the recorder
holds; the friendly name is resolved only when something has gone wrong. When
the endpoint cannot be found at all the id is still shown — a device that has
disappeared explains an empty recording too.

internal/audio/devices.go

@@ -101,3 +101,30 @@ func endpointName(dev *wca.IMMDevice, fallback string) string {
 	}
 	return fallback
 }
+
+// DeviceName resolves an endpoint id to its friendly name.
+//
+// Diagnostics quote the id that was CONFIGURED, which is a GUID — an operator
+// told "no audio at all from {0.0.1.00000000}.{6a27abfd…}" learns nothing they
+// can act on, while "no audio at all from DAX RX 1 (FlexRadio DAX)" points
+// straight at the DAX panel.
+//
+// Falls back to the id when the endpoint cannot be found, which is itself worth
+// seeing: a device that has disappeared explains an empty recording too.
+func DeviceName(id string) string {
+	if id == "" {
+		return "(none)"
+	}
+	for _, list := range []func() ([]Device, error){ListInputDevices, ListOutputDevices} {
+		devs, err := list()
+		if err != nil {
+			continue
+		}
+		for _, d := range devs {
+			if d.ID == id {
+				return d.Name
+			}
+		}
+	}
+	return id
+}