Add database migration system

[rsslldnphy]

Summary

• Adds a complete migration system that diffs TypeScript schema config against the live database, generates SQL migration files, and runs them with safety checks
• Schema diffing engine compares config state vs database state via a normalised SchemaSnapshot intermediate representation
• Safety classification (inspired by strong_migrations gem) warns on unsafe operations like dropping tables/columns or unsafe type casts
• Migration runner uses PostgreSQL advisory locks to prevent concurrent migration runs across app instances
• Tracks applied migrations in _orm_migrations table with SHA-256 checksum verification
• Supports non-transactional migrations (e.g. CREATE INDEX CONCURRENTLY) via -- orm:no-transaction directive
• CLI: orm generate migration --name <desc>, orm db migrate, orm db migrate status
• Programmatic API: migrate.generate(), migrate.run(), migrate.status() for app-startup usage
• Enhances getForeignKeys to return onUpdate/onDelete actions
• Enhances getUniqueConstraints to return structured column data and nullsNotDistinct

Test plan

• Existing orm-migrate tests pass (67/67)
• Existing orm-cli tests pass (100/100)
• Both packages build cleanly with no type errors
• Unit tests for new migration modules (diffSnapshots, operationToSql, checkSafety, safeCasts, files, configToSnapshot, pulledToSnapshot)
• Integration tests with database (generate, run, status, locking, tracking)

🤖 Generated with Claude Code

[github-actions]

Coverage Report

• orm-cli: 96.85%
• orm-migrate: 94.02%
• orm: 98.47%
• sql: 96.93%
• toolbox: 100%