Relocates LibraryState (struct + impl), CleanupResult, BackfillReport,
LibraryAlbumMetadataUpdateRequest, and LibraryAlbumTrackMetadataUpdate
from library/commands.rs to a new library/state.rs module.
These types are consumed by commands_v2/library.rs,
commands_v2/legacy_compat.rs, commands_v2/mixtapes.rs,
commands_v2/link_resolver.rs, cast/commands.rs, and
session_lifecycle.rs. The existing pub use re-exports in
library/mod.rs are updated to source from state, and commands.rs
re-exports them in turn so historical
crate::library::commands::* paths (still used by
commands_v2/legacy_compat.rs, which is out of scope for this task)
continue to compile.
This unblocks future deletion of library/commands.rs once the
remaining #[tauri::command] definitions there are inlined into
their commands_v2 callers (separate task).
No serde shape changes; struct fields, derives and serde
attributes are preserved verbatim, so the JSON the frontend
receives is identical.
cc
vicrodh
e0dc464a65