feat(drag): native DAW drag from Water Studio on Mac + Windows

Mac: remove guard that silently dropped drag when file not cached —
WMDragFileProvider now handles lazy download during the drag gesture.

Windows: inject fetch interception to cache audio on play/hover,
add morphDragStart IPC + contextBridge so mousedown+move triggers
native OS startDrag via Electron event.sender.startDrag().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: grauxmusic