Wires AmazonClient into the metadata source registry following the
exact same pattern as DeezerClient. No existing source paths touched.
- Add get_album_metadata / get_artist_info / get_artist_albums_list
aliases to AmazonClient (mirrors DeezerClient interface aliases)
- Register amazon in METADATA_SOURCE_PRIORITY and METADATA_SOURCE_LABELS
- Add _get_amazon_factory() + get_amazon_client() to registry.py
- Add amazon branch to get_client_for_source(); thread amazon_client_factory
kwarg through get_primary_client() and get_primary_source_status()
- Re-export get_amazon_client from the core.metadata_service shim
- Add Amazon Music option to Settings metadata source dropdown
- 3530 tests pass
1f579cede8