Tags: tomLadder/thermoprint

Add print-template CLI command for JSON-based label printing

Enables AI agents and automation to print labels by describing elements
(text, QR codes, barcodes, shapes) in a simple JSON format. Renders
templates to SVG and rasterizes via sharp. Supports both a simplified
flat-props format and the full web editor export format.

Also moves mmToPx/PX_PER_MM to core as single source of truth.