Add an SFZ Builder, target architecture, and CI

[sastraxi]

This PR does a lot, so appreciate your patience. Three things:

1. An on-device SFZ builder so users can create samplers with sfizz and their own samples
2. A target architecture (frontend-architecture.md) meant for modernizing the stack
3. Github actions for some sanity checks

SFZ builder

Built to create sampler banks for pads, which are generally wired as contiguous blocks of MIDI notes. Allows drag-and-drop from the device's audio files / audio files on an inserted USB. SFZ banks are saved in the appropriate device folder (File Manager), with samples copied in so that banks can be shared by simply copying the whole folder.

Uses sane SFZ defaults (one shot / unity gain / no time shifting), which probably needs some tweaking.

Target architecture

Purely vibe-coded rules to try to make it easier to build self-contained "apps" with modern Javascript. The implicit decision here is that we're not trying to upstream our changes, which I think is worth a conversation to make sure we're on the same page.

[rreichenbach]

Cool stuff. Can't justify reviewing the actual code, but looks like it should be safe to merge.