fix: dj.mjs — declare spinSpeed at module level (ReferenceError)

Co-Authored-By: Claude Opus 4.6 (1M context) <[e-mail]>

fedac/native/pieces/dj.mjs

···
 let frame = 0;
 let lastUsbCheck = 0;
 let usbConnected = false;
+let spinSpeed = 0;      // record spin rate (0=stopped, 1=playing)
 let scratchSpeed = 0;   // current scratch velocity (-2 to 2)
 let wasPlaying = false;  // was playing before scratch started