Generate Database Migration from Schema Diff

Compare the current database schema with the desired schema below and generate a safe migration. Include:

1. **Up migration:**
   - ALTER TABLE for column additions, modifications, drops
   - CREATE TABLE for new tables
   - CREATE INDEX for new indexes (CONCURRENTLY where possible)
   - Data transformation queries if column types change
   - Constraint additions (FOREIGN KEY, CHECK, UNIQUE)

2. **Down migration (rollback):**
   - Reverse every change in the correct order
   - Data preservation queries before destructive changes

3. **Safety checks:**
   - Wrap in a transaction
   - Add IF EXISTS / IF NOT EXISTS guards
   - Comment potential data loss operations
   - Estimate lock duration for large tables
   - Flag any operations that require downtime

Desired schema changes:
[DESCRIBE YOUR CHANGES]

Current relevant schema:
[PASTE CURRENT SCHEMA OR LET @workspace FIND IT]