Inlines the bodies of `library_update_folder_settings` and
`get_track_by_path` from crate::library::commands::* directly into
commands_v2/legacy_compat.rs. Maps the legacy String error type to
RuntimeError::Internal at every return path.
Deletes the legacy #[tauri::command] definitions in
library/commands.rs. The data-layer methods on LibraryDatabase
(update_folder_settings, get_folder_by_id, get_track_by_path) are
unchanged.
No frontend invoke changes required.
Step 6 of the legacy cleanup plan, group F (folder settings + track
lookup).
cc
vicrodh
145b589c2a