qbzd login: interactive OAuth via system browser. Opens browser,
captures callback, exchanges code, saves token to keyring. Same
flow as desktop app. Daemon auto-logins on next start.
Library scan endpoint (POST /api/library/scan): discovers audio
files in registered folders. Full metadata extraction deferred
until MetadataExtractor moves to qbz-library crate.
Service files: systemd, OpenRC, runit + example qbzd.toml config.
cc