- Relocate the shared metadata helper module from core/metadata_common.py into core/metadata/common.py.
- Update the new metadata package, the import pipeline, and the web entrypoint to use the package-scoped helper.
- Keep the shared config, mutagen, file-lock, and tag-writing helpers centralized without touching unrelated files.
- 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
