CAN should fire a SCRATCHFILE_FOUND event when an existing scratchfile is found

CAN may look for existing scratchfiles at different stages in the future. When one is found, a SCRATCHFILE_FOUND event should be fired, with the path of the scratchfile as an argument.

Backlinks

• CAN should begin watching an existing scratchfile on startup
  • CAN fires a SCRATCHFILE_CREATED event. This is a similar but distinct event whic may repeat in multiple contexts if CAN allows multiple scratchfiles in the future - SCRATCHFILE_FOUND. CAN should fire a SCRATCHFILE_FOUND event when an existing scratchfile is found. CAN's watch-scratchfile handler should listen to the SCRATCHFILE_FOUND event.