Database models and migrations

[troyscott]

Description

Set up SQLModel ORM with Alembic migrations connecting to Azure SQL via managed identity.

Key points

• Connection via managed identity (no passwords): azure-identity + pyodbc
• SQLModel for Pydantic + SQLAlchemy integration
• Alembic for schema migrations
• Seed data script for initial setup

Acceptance criteria

• SQLModel models defined
• Alembic configured with migration scripts
• Connection uses managed identity in Azure, connection string locally
• Seed data script creates initial records
• Migrations run as part of deployment