Prefer MetaDataStore for activity metadata reads

Activity Browser keeps an in-memory MetaDataStore (app.metadata) so UI and results code can look up process labels without per-row SQLite. Prefer that store for reads (names, products, locations, units, and other stored fields). Do not query ActivityDataset or bd.get_node for display metadata the store already has. Mutations still go through Brightway APIs; fall back to Brightway only for missing rows, fields the store does not keep, or a live activity proxy. Helpers in bwutils/ should take a dataframe or lookup callback rather than importing app.