Migrate `qbzd scrobble login|status|enable|disable` off the interim custom
`crate::scrobbler` (scrobbler.json) onto the canonical
`qbz_app::settings::scrobblers::ScrobblerSettingsStore` (SQLite at the daemon
data root) — the SAME store the scrobble-on-play engine reads and the settings
bundle export/import already carries, so credentials are consistent across the
daemon, the desktop store format, and bundle transport. Session keys / tokens are
registered with `qbz_log::register_secret` before they touch the store.
enable/disable now refuses a not-connected provider up front (`not_connected`)
and status reads `lastfm_is_authed()/active()` from the store snapshot.
This was the orphaned tail of the store migration the scrobble-on-play engine
and TUI screen already build on; committing it closes the gap.
cc
vicrodh
88af1b248b