Function start_live_spectrum_stream 

pub fn start_live_spectrum_stream(
    window: Window,
    audio_service: State<'_, Mutex<AudioService>>,
    stream_state: State<'_, SpectrumStreamState>,
) -> Result<(), String>

Starts (or restarts) push-based live spectrum streaming for the calling window.

Behavior:

• Captures the current shared SpectrumTap from AudioService.
• Signals any previously running stream task to shut down using that task’s own cancellation flag, then replaces it.
• Spawns a background loop that analyzes the tap and emits live-spectrum events at STREAM_INTERVAL_MS cadence.
• Automatically exits when event emission fails (for example, when window closes).