Database Migration Writer

Write a database migration for the following change:

Change: {{migration_description}}
ORM: {{orm_name}}
Current schema: (read from {{schema_file_path}})
Database: {{database_type}}

Requirements:
1. Generate both the schema change (ORM model) and the raw SQL migration file
2. Handle the migration safely:
   - Add columns as nullable first if they'll be NOT NULL (backfill, then alter)
   - Use IF NOT EXISTS / IF EXISTS guards where supported
   - For column renames, use a two-step approach in prod (add new, migrate data, drop old)
3. Include a rollback/down migration
4. If adding indexes, consider:
   - CREATE INDEX CONCURRENTLY for large tables (PostgreSQL)
   - Composite index column ordering (most selective first)
5. If the table has RLS enabled, update policies if the new columns need them

After writing the migration:
- Estimate the impact on a table with {{row_count}} rows
- Flag any operations that will lock the table
- Note if this migration is backward-compatible with the current application code