Database Schema

Design database schema for: [FEATURE/DOMAIN]

Please provide:

1. **Models**
   - Table name
   - Columns with types
   - Rails migration commands

2. **Associations**
   - has_many, belongs_to, has_one
   - Through associations if needed
   - Polymorphic if needed

3. **Validations**
   - Required fields
   - Uniqueness constraints
   - Format validations

4. **Indexes**
   - Foreign keys
   - Unique indexes
   - Composite indexes for common queries

5. **Considerations**
   - SQLite3 limitations (no JSONB, array columns)
   - Data integrity (NOT NULL, defaults)
   - Future scalability

Output as Rails generator commands.