- Keep existing metadata_cache and metadata_service at the top level for now
- Move the new branch-local metadata helpers under core/metadata
- Share MusicBrainz release cache state from core.metadata.source and update import sites
- Move import flow modules into a dedicated package
- Update app and test imports to the new namespace
- Group the import-focused tests under tests/imports
- remove stale wrapper helpers from web_server and metadata_common
- import provider helpers directly in metadata_source
- keep the metadata modules' public surface explicit
- remove runtime from metadata helper APIs where it only carried config, logger, mutagen, and database access
- keep runtime only for the source-ID enrichment path that still needs live worker handles
- add the new metadata helper modules and update the tests to match the slimmer interfaces
