Possible to create double notes in pencil mode on piano roll

[Dan-McElroy]

Describe the bug
When drawing in notes in pencil mode, it's possible to layer notes on top of each other. If two notes are layered, then when playing through the browser the output will be twice as loud, and it can also lead to confusion when you delete a note and another note remains in its place.

This applies to both rhythm and non-rhythm tracks.

To Reproduce
Steps to reproduce the behavior:

1. Open the piano roll for any instrument
2. Draw in a note anywhere
3. Draw in a second note at the same time, one note below or above, and then drag this note on top of the first note
4. Play the piano roll and observe that the "doubled" note plays louder than other notes at similar velocity
5. Delete this new note and observe that the original note remains underneath it

Expected behavior
The new note overwrites the original note or, in the case of the new note starting later than the original note, the original note is resized to end at the beginning of the new note.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop:

• OS: MacOS
• Browser: Firefox
• Version: 130.0.1

[Dan-McElroy]

I just discovered this app and have been having a blast with it, it's great to get down ideas when I'm on the move and away from my DAW. Just noticed this minor issue and had a glance at the related code, my first idea to fix it would be on mouseup, to check for notes in the same track within the range occupied by the just-created note and resize or delete any existing notes as needed. I'll try to take a closer look later, too.