feat: Migrate gallery report generator.

[nedseb]

Description

Move the gallery README generator from micropython-steami-tutorials.

Source

micropython-steami-tutorials/generate_report.py (267 lines)

Tasks

• Copy generate_report.py
• Adapt paths for new repo structure
• Verify HTML gallery generation produces same output
• Add CLI documentation in README

Features

• Extracts METADATA dict from screenshot.py (title, widget, description)
• Generates HTML table (2-column layout) with side-by-side SVG ref + sim PNG
• SSIM score badges
• Outputs to docs/mockups/README.md

Dependencies

• feat: Migrate PC validation pipeline (validate.py). #4 — validate.py must be migrated first

Parent

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