18 skills/commands still reference old Microsimulation API instead of policyengine.py Simulation

[nikhilwoodruff]

The codebase has moved to policyengine.py with from policyengine.core import Simulation, ensure_datasets(), etc. But 18 files still reference the old Microsimulation class from policyengine_us/policyengine_uk:

• skills/tools-and-apis/policyengine-microsimulation-skill/SKILL.md
• skills/tools-and-apis/policyengine-interactive-tools-skill/SKILL.md
• skills/technical-patterns/policyengine-vectorization-skill/SKILL.md
• skills/technical-patterns/policyengine-testing-patterns-skill/SKILL.md
• skills/technical-patterns/policyengine-review-patterns-skill/SKILL.md
• skills/domain-knowledge/policyengine-us-skill/SKILL.md
• skills/domain-knowledge/policyengine-uk-skill/SKILL.md
• skills/domain-knowledge/policyengine-healthcare-skill/SKILL.md
• skills/documentation/policyengine-writing-skill/SKILL.md
• skills/documentation/policyengine-plugin-maintenance-skill/SKILL.md
• skills/data-science/policyengine-us-data-skill/SKILL.md
• skills/data-science/policyengine-uk-data-skill/SKILL.md
• skills/analysis/policyengine-district-analysis-skill/SKILL.md
• skills/analysis/policyengine-analysis-skill/MICROSIMULATION_REFORM_GUIDE.md
• skills/README.md
• commands/backdate-program.md
• agents/country-models/implementation-validator.md
• ECOSYSTEM.md

The only skill with correct imports is policyengine-simulation-mechanics-skill. All others should be updated to use from policyengine.core import Simulation and ensure_datasets() patterns.