Fix EuroMLSys template: sigplan format with proper acmart.cls

- Was: raw acmart.zip (ungenerated dtx), no main.tex
  → Writer created sigconf main.tex with "Conference'17" header
- Now: generated acmart.cls + ACM-Reference-Format.bst + sigplan main.tex
  → \documentclass[sigplan,10pt,nonacm]{acmart}
  → Proper two-column sigplan layout, no ACM branding

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: JihaoXin