Add change-request doc: machine cleanup and filament research

Handoff doc for the other AI working this site — decommission ShopSabre
23 and the Box & Pan Brake (with every downstream reference to clean
up), verified manual/tutorial links for five machines, and reference
data for all 28 filaments the lab has actually purchased.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: allengregoryiv