Function resolve_db_path 

pub fn resolve_db_path(
    cli_db: Option<PathBuf>,
    config: &BhtuneConfig,
    xdg_data_home: Option<&str>,
    home: Option<&str>,
    appdata: Option<&str>,
    is_windows: bool,
) -> PathBuf

Resolve the database path with CLI flag > env var > config file > platform default precedence. The env var is already folded into cli_db by clap’s env attribute on Cli::db; the platform-default tier takes its own raw environment values (rather than reading std::env internally, like default_db_path_from) so this stays fully unit-testable without touching real process environment variables.