Perform a proper synthesizer reset

[spessasus]

Per MIDI specification (RP-15), Reset All Controllers message does not actually reset all channel controllers. More importantly, it doesn't global parameters such as chorus, drum status and MIDI system.

This PR adds a GS reset after, ensuring that the synthesizer fully resets into a fresh state when loading a new song.
While most MIDI files do have a reset at the start, some don't and this PR fixes them.

CC @ryohey @robertnhart

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Project	Deployment	Actions	Updated (UTC)
signal	Ready	Preview, Comment	May 20, 2026 2:18pm

[robertnhart]

I did a simple test with the Preview version. I set Signal to output to a virtual MIDI cable, then I connected the virtual MIDI cable to a MIDI monitor app. It looks like the reset code gets called when I open a new file.

If you are using Signal with an external MIDI device, perhaps you might not want Signal to send a GS Reset every time you open a new file. I wonder if this behavior might cause confusion or problems for some users (?).

[spessasus]

I don't think that's an issue, esp given that most files I have already have a GM/GS/XG reset at the start.
It'll be more confusing without it, as signal already reset the synth via CC, but only partially, so it was really confusing that things like controllers reset but pitch wheel range, tunigns, etc. didn't.

[ryohey]

That seems reasonable, thanks!