feat: Migrate PC validation pipeline (validate.py).

[nedseb]

Description

Move the SSIM-based validation pipeline from micropython-steami-tutorials.

Source

micropython-steami-tutorials/validate.py (269 lines)

Tasks

• Copy validate.py
• Adapt paths for new repo structure
• Verify python validate.py produces same SSIM scores as before
• Add CLI documentation in README

Features

• Discovers tutorials by scanning screenshot.py files
• Runs screenshot.py → generates simulator PNG
• Rasterizes SVG reference via cairosvg
• Computes SSIM (structural similarity) score
• Generates amplified diff images (5x)
• Threshold: SSIM >= 0.85 or pixel-MAE >= 0.95

Dependencies

• feat: Migrate Pillow simulator (sim_backend). #3 — SimBackend must be migrated first

Parent

• feat: Scaffold repo and migrate simulation/validation tools. #1 — Migration umbrella issue