ADR-0002: Database and Alembic (SQLite-first)

Status: Superseded by ADR-0017

Weir uses file-backed SQLite as its primary database with Alembic for schema migrations. No external database service is required.

Later change: ADR-0017 moved the backend to C# / .NET 10 in apps/server (the Python apps/backend was removed in #523). SQLite stays, but schema changes are now numbered SQL migrations in the .NET server; Alembic is no longer used, and a database the Python backend created is not a Weir database. The server keeps the alembic_version table name for its own revision record, so databases Weir created open unchanged.

Full ADR source: docs/adr/ADR-0002-database-sqlite-alembic.md