Add Spectral selection frequencies indicators

### Problem to be solved

currently we have no feedback about the frequency selection when doing a spectral selection, we only have time selection

### Your idea

when on a track with spectrogram visualisation or multi-view

we should show near the time selection indicator the trio frequency values of the current spectral selection
- start frequency
- center frequency
- end frequency

### Prior art

_No response_

### Additional context

_No response_