Replace three separate XML metadata files (info, drawing-info,
plate-info) and per-plate G-code placement files with a single
nest.json inside the ZIP archive. Programs remain as G-code text
under a programs/ folder.
This eliminates ~400 lines of hand-written XML read/write code
and fragile ID-based dictionary linking. Now uses System.Text.Json
with DTO records for clean serialization. Also adds Priority and
Constraints fields to drawing serialization (previously omitted).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
