Add MIDI input support for synth and control workflows

[ctoth]

Summary

There is no apparent Web MIDI integration for driving synth playback or control changes.

Verification

Verified by source and README audit.

Relevant evidence:

• No requestMIDIAccess / MIDI references in src/ or README.md

Why this matters

For a browser audio library with synth support, MIDI note/control input is a common integration point for instruments, sequencers, and live-control tooling.

Expected behavior

Expose a MIDI integration layer or helper API for note on/off, CC mapping, and device hookup.