Fix deadlock on exit by making mic level updates async

cmd/tui/model.go

@@ -337,7 +337,8 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 
 				// Update mic level for display (use the calculated level)
 				if m.program != nil {
-					m.program.Send(micLevelMsg(level))
+					// Use goroutine to prevent blocking the capture loop if the UI is busy (e.g. shutting down)
+					go m.program.Send(micLevelMsg(level))
 				}
 			})
 			m.addLog("Audio capturer initialized")