refine(skills): lang-sql-dev - expand pillar coverage (2/8)

[aRustyDev]

Summary

lang-sql-dev has 2/8 pillar coverage and needs expansion.

Current Coverage

• ✗ Module System
• ✓ Error Handling
• ✗ Concurrency
• ✗ Metaprogramming
• ✗ Zero/Default Values
• ✓ Serialization
• ✗ Build/Dependencies
• ✗ Testing

Refinement Checklist

• Add Module System section (schemas, namespaces, views)
• Add Concurrency section (transactions, locking, isolation levels)
• Add Metaprogramming section (dynamic SQL, stored procedures)
• Add Zero/Default Values section (NULL handling, COALESCE, DEFAULT)
• Add Build/Dependencies section (migrations, versioning tools)
• Add Testing section (unit tests, fixtures, test databases)
• Run just validate-pillars lang-sql-dev to verify coverage
• Ensure SKILL.md is under 500 lines (use progressive disclosure)

Validation Command

just validate-pillars lang-sql-dev