Function migrate_if_needed 

pub fn migrate_if_needed(
    db_root: &Path,
    object_store: &ObjectStore,
    id_index: &IdIndex,
    sorted_indexes: &SortedIndexes,
    graph: &GraphStore,
    dek: Option<&Dek>,
) -> Result<bool, Error>

Run the full v1 → v2 migration for one database directory.