Context

src/commands/db.rs contains two #[cfg(feature)] URL validation branches:

• #[cfg(feature = "postgres")] — rejects non-postgres URLs
• #[cfg(feature = "sqlite")] — rejects postgres URLs

These branches are not covered by any unit tests because they require compile-time feature selection, making them invisible to the default test run.

Acceptance Criteria

• Unit tests for the postgres validation branch compiled under --features postgres
• Unit tests for the sqlite validation branch (default features)
• Both happy-path and error-path covered
• Tests added to src/commands/db.rs #[cfg(test)] block

Notes

The fix lives in src/commands/db.rs. The validation uses zeph_db::is_postgres_url() which is already unit-tested in zeph-db. These tests would verify the integration with handle_db_migrate().