Context

src/init.rs build_config() gained a postgres branch in Phase 3: when state.database_url is Some(_), it skips the sqlite_path prompt and sets MemoryConfig::database_url. This path has no build_config unit test.

Acceptance Criteria

• Test that when WizardState { database_url: Some("".to_owned()), .. } is passed to build_config(), the resulting Config::memory.database_url is Some(_)
• Test that sqlite_path falls back to the serde default (not an empty string) in that case
• Test that when database_url is None, the existing sqlite path behavior is unchanged

Notes

WizardState derives Clone under #[cfg_attr(test, derive(Clone))] and has Default impl — test setup is straightforward.