refactor: Remove sim/ and tools/ after migration to steami-tools.

[nedseb]

Description

After the simulation and validation tools are migrated to micropython-steami-tools, these directories become redundant.

Tasks

• Delete sim/sim_backend.py and sim/ directory
• Delete tools/board_validate.py and tools/ directory
• Delete validate.py
• Delete generate_report.py
• Delete docs/mockups/ (moved to tools repo)

Blocked by

• feat: Scaffold repo and migrate simulation/validation tools. micropython-steami-tools#1

Parent

• refactor: Remove library and tools after migration to dedicated repos. #1 — Cleanup umbrella issue