Display note counts per instrument in song details

[Bentroen]

In the Songs page, by the 'Instruments' or 'Notes' attributes in the song stats display, show a question mark button as follows:

When clicked, this shows a modal similar to Note Block Studio's song stats, showing the number of note blocks per instrument (including custom instruments):

These stats are already calculated and stored in the database as part of the stats subdocument, and even already sent to the front-end server at render time. As such, implementing this is a matter of displaying them properly in the SongDetails component:
https://github.com/OpenNBS/NoteBlockWorld/blob/main/web/src/modules/song/components/SongDetails.tsx#L101-L113

Alternatively, instead of a modal, an expandable/collapsible section may be added inline to the stats table, if it improves presentation.